Can they force me to work full time?

I worked for a Mental health institute for almost 7 years. When I began there, I worked 2 days a week. Shortly thereafter I accepted 3 days a week, then they wanted 5 days a week, and I explained that I could not I do 5 days a week because I have Fibromyalgia, and I really need that 1 day for massotherapy and just relaxing, so I can control my pain without taking so much medication and being wasted by the end of the week. They said ok, we'll try 4 days.

In Nov. they came to me and said "our job is now 5 days a week." I said, "I told you I cannot do that because it causes me too much pain" (it's a very stressful place to work). They said, "Well, when is your last day then?" I had my doctor put in writing that I could not work 5 days a week and gave it to them. So in December I was let go. Now I cannot collect unemployment because I cannot work 5 days a week. My pain is worse because of the stress, and I am basically screwed. Can they do that?