That's frustrating! I know what you mean. Just because it doesn't show and we have good days, people forget that we have Fibro. I had my husband read a website on Fibro and he was really understanding but at times, he seems to forget. He starts a home project and ask me to clean after him like before when I was in less pain. I have to remind him from time to time.
If you can, print description of Fibro and make your family read it and tell them that if they see you ok one day, it doesn't mean you are pain free, it means that it's tolerable that day but the next day might be the opposite.
I hope you can find some support. This is so important.
Good luck.