I don't think you are over reacting at all. The bad thing about
these kinds of illnesses is that they are often "invisible" to other people and it's hard for some people to really understand the daily struggles we go through. Things that healthy people take for granted are a huge struggle for us. It's not as simple as getting up in the morning, taking a shower, getting dressed, etc. Just sitting up in the morning and getting your feet on the ground in the morning can be hard to do.
Something you might want to have your husband read is the Spoon Theory and you can find it at http://www.butyoudontlooksick.com Once you get to the sight, just click on the Spoon Theory on the menu bar to the left of the page. It is written by a woman who has lupus and she does a great job of explaining what it is like to live with a chronic illness everyday. I printed out several copies and had my family and close friends read it. Hopefully it will help your husband to be more understanding.
I hope your rheumatologist appointment goes well. Hang in there.