I'm sorry you find yourself to be in such difficult circumstances.
At the end of your post you asked what self-care is. And I think that's an interesting question... not that I think I know the answer.
I think, for me, self-care involves simply figuring out what you need as well as what you can do to make yourself as content as possible. Notice I didn't say "as happy as possible". I think for a lot of us, myself included, happiness is something that really just isn't even in the cards, so to speak; and the best we can hope for is to be able to say: "ya know... not everything in my life is the way I'd like to have it. But, all things considered, it's okay."
How one reaches that point of contentment probably varies from one person to another. For some people self-care may include meditation and / or physical activity, community service to build self-esteem. For someone else it may include a bubble bath or relaxing in a whirlpool tub. A hobby, of some sort, might be included as well I suppose. Self-care is going to be different for each individual depending on their circumstances I would presume. At least those are my thoughts with regard to your question. Best wishes...