What Causes Severe Pain In The Leg Muscles While Suffering From Fibromyalgia?

I have a lot of health issues, RA , diabetes, fibromyalgia , hypertension , the RA is really attacking my body since November , they took me off Embrel and put me on Humira my body feels like the muscles are dying , I worked two days, and my body felt like I was ran over by a truck, and was off work 6 days trying to build up my body they had me on 60 mg of prednisone then 50 ,40,30,20,10, I then went back to work Monday and then Tuesday started feeling a little weak, then Wednesday my legs were exhausted but I continued to work at a slower pace, at the end of my shift I could barely walk to my vehicle , and can t work today, my legs are throbbing of muscle pain and I m allergic to a lot of medications