I'm not a mom myself, I'm helping my brother raise his two daughters, but I do have fibomyalgia and chronic migraines and I can sympathize with your situation.
My two nieces are old enough now (8 and 10) to understand when I am in pain and need some help. For example, when their dad is out of town, and I'm staying at their house, they have a chart of chores that need to be done before and after school. they're really good about doing them, because they know that it helps me, AND if they do all the chores quickly, they get down time on the sofa with me, playing a game or watching a movie.
I've also learned that when I make meals that I need to make extra so I have leftovers for later in the week or to freeze for later in the month. That way, when I'm having more pain than usual, I can pull out leftovers and not have to put a lot of energy into cooking. Again, the kids have learned how to help in the kitchen.
Sometimes, it's best to realize that you need to let some of the little things go so you can spend more time with your family. Your house doesn't really need to be perfectly clean...it's really more important to spend time with your family that to have a sparkling bathroom, right? :) Just do what you have the energy for and call it good. Remember, if your kids are old enough, have them help you as much as possible.
I know how hard it can be too live with chronic pain. I've had to learn over the years that I need to ask for help. Do you have friends, neighbors or a church community you can ask for support (chores, meals, errands, etc)? It can be humbling to ask for help, but sometimes when we have overwhelming long term pain we just need some help.
Another thought. I wonder if there are some agencies in your area that can provide you some support? I don't know your exact needs, but you might want to go online and see what is available.
Anyway, I don't know if this is the advice you were looking for, but I hope it helps. Feel free to PM me if you want to talk more. Good Luck!