Wow, that's a lot in a short paragraph. My first reaction was to just take a minute to acknowledge (for myself) how monumentally different your lived experience of all of these things must be from my experience of sitting at my desk reading a list that is seemingly so itemized and contained. I feel like it's so easy for us to imagine what life is like for someone else, and forget that what we imagine may bear no resemblance to the other persons experience. I offer that first response in place of anything like "that must be so hard" and "I'm so sorry". I also offer it as a way of acknowledging the extra burden that people are asked to carry when their bodies change in ways that are visible to the rest of us.
When we lose our hair or parts of our bodies, when we start walking slower, or talking quieter, when we transgress that most feared and loathed of societal rules by not appearing skinny, automatically there is a social expectation that we are responsible for explaining it to others. It magically becomes our job to make others feel comfortable and apologize for not fitting into their expectations. This is ableism in action, and it is connected to everything we feel about ourselves. It's easy to forget about this social piece. Messages about what makes a good body and a bad body, even though they are always specific to time and place, are so ubiquitous and insidious, that we come to feel as if the way we feel privately about our bodies is only a reflection of ourselves. It isn't. It's a reflection of the world around us that determines (based on factors that have nothing to do with happiness, pleasure, acceptance, or justice) the right way and wrong way for a body to respond to this world.
None of this may make you feel any better, but it seems important to at least acknowledge that there are social and political elements to how we end up feeling about ourselves. Doing so can help us feel less isolated, and for some people it's a part of working toward feeling differently about their bodies and lives.
But you didn't ask for a lecture on ableism or systemic oppression, and if you're still reading this, let me try to offer you something that you asked for, namely tips.
Keeping in mind that tips are, at best, ideas that will inspire you to act in ways that fit your own life, values, and circumstance, and at worst they are decontextualized roadside opinions that make you feel worse, here you go:
Get a Lay of the Land
If no one has talked to you about it yet, you may want to learn about some of the predictable ways that breast cancer and treatment impacts sexuality. Most of the information that comes from doctors is presented in a normative framework, so they will tell you what happens for 'most' people, and what you might expect to happen to you. Keep in mind that your experience may or may not fit others. Still, for some it can be helpful to get a sense of what people over time have documented.
Start with What You Know
Because of your experiences with vulvodynia, you went into diagnosis and treatment with plenty of experience of how bodies can make sex harder, and how if you want to experience sexual pleasure you have to get creative with your ideas of what sex is. Since you mentioned being happy with your body, I'm guessing you have already had some success in learning to love a body that is causing you pain and aggravation. You probably have more internal resources than other people for whom breast cancer is their first experience of physical pain or significant body difference. I would probably want to ask you more about that, about how you came to be pretty happy with your body while also experiencing vulvar pain for so many years. There may be lessons you've already learned that could be helpful to you now.
If You Can't Love Your Body, Try to Like Parts of It
In terms of "loving your body" my first tip is to never use the term "love your body" again. I'm being only half serious here. If it works for you to talk about wanting to love your body, then you should. But it feels to me like a statement that is already laden with pressure and expectation. I'm not arguing that it would be better if we all loved our bodies, but a) I'm not sure I fully understand what we mean by loving our bodies, and b) for many of us the very concept seems so foreign, that being told it's necessary for healthy sexuality is like being told you'll never be sexually happy.
Forgetting about the language for now, working on how you feel about your body is, as you probably know, more of a marathon than a sprint. But you have to start somewhere. Here's one tip. Sometime today, try to find one part of your body that you like. It can be large or small, a whole thing or just part of a thing. Think about what you like about it. Is it the shape? Is it the way that part looks when you move? Is it the way it feels? Now say it out loud. Say that you like X, and why. Don't worry if it's a part that you also hate some of the time, just pick something that works now. If you prefer or need to communicate in other ways you could draw a picture of that part of your body, or sing a song about it. If you can touch that part on your own, spend a few minutes touching it. If you have someone else who can touch you there (and it's not going to be crossing a boundary to have them touch you there) ask for a five minute massage of that area. Don't force any of this, only do way feels comfortable and safe, but also, don't expect miracles. Do this once a day. Try to do it every day. It's a start.
Talk with Your Partner
If you are in a relationship, try to have at least one conversation with your partner about sex. If you aren't talking about sex already, the first conversation doesn't need to be about anything other than setting some guidelines about future conversations about sex. So if your partner has questions, desires, concerns, do you want them to keep it to themselves, or talk with you? And what do they expect from you? Remember that even if you aren't feeling sexy or sexual, your partner may still be turned on by you and may be in fact frustrated by the lack of sex. If you're committed to staying together, there are plenty of ways of getting both of your needs met (that don't involve either of you having sex when you don't want it). But you can't figure that out if you don't talk about. If you can avoid putting pressure on yourself, or being down on yourself because you don't feel like sex, remember that in every relationship people will have times when they want more sex than their partner. This may be one of those times when you can't give them what they want. And there will eventually be a time when the situation is reversed. This brings me to my last tip…
Give Yourself a Huge F-ing Break
That's right, it's worth swearing for this final tip. Between social expectations, expectations and demands from loving, well-meaning friends, family, and partners, and your own experience of worrying about your health, figuring out your body, and dealing with pain and fatigue, this is one of those times when life is extra hard. So forget about living your best life, forget about trying to be happy or strong or heroic. Unless those things genuinely give you pleasure or strength, try to do your best to give yourself an enormous break and a wide berth when it comes to getting by day-by-day. You aren't going to be feeling like this forever. Life is always changing. And one of the very simplest things to do (which can also be really difficult) is not to kick yourself when your down.
Thus ends the tips on how to deal with body image and sex when you're feeling the way you're feeling. I hope this has been a little helpful, and as always, if you have any other questions just let me know.