What Causes Swelling In The Knees When Diagnosed With Fibromyalgia?

I have swelling behind both knees and it is uncomfortable. I have fibromyalgia, rls, cfs, and am receiving radiation for breast cancer that was removed in March. I also have lymphedema and cellulitis in my right arm. Both occurred after the surgery. I have taken 2 courses of anitbiotics for the cellulitis but it is still slightly pink. Also found out that the second antibiotic had sulphur in it and I guess I am allergic to sulphur now. The rash started 3 days after I started taking the second antibiotic (last Sunday was the day the rash started and I still have the rash now. I have no other known allergies. Each day that I went for radiation, the rash got worse, so I skipped the radiation on Thurs. and today. It is better on my torso, arms and legs, but my face and neck are beat red. Looks like a bad sunburn but I have not been in the sun. I feel totally exhausted but can t sleep because I just can t get comfortable. Are all of these symptoms relatable to the cellulitus or the lymphedema?