Suggest Treatment For Rash On Legs

Hi Doctor, I have had a distressing rash form that started on my lower legs and then went up past the knee, then started on the wrists and now is all over both arms and legs. It is itchy. My left leg, on which I had melanoma 7 years ago, is usually a bit swollen due to removal of some nodes from the groin after a sentinel node byopsy, and I have been found clear of any other bad moles, but the lyphedema is the worst it has been in years, with a large pocket in the groin. My right leg, which is normally fine, is somewhat swollen too. Stand up or sitting is painful, and walking is difficult. I have taken Benadryl tablets which have reduced the itching a bit and acetamenophen for the pain, and the swelling goes up and down and the rash is sometimes worse than others. Any suggestions?