Suggest Treatment For Shoulder And Neck Aches And Rashes In That Area

After neck/should ache for 5 days started home treatment with Thermacare on shoulders and lower blades. 2 days later scattered hivey rash started around underarms and shoulders. 3rd day spread on most of body but was red and smooth, like from sun exposure. Especially under arms, groin, buttocks, upper thigh, behind knees, bottom of forearms. Went to doctor. Doesn't know. Doing blood test. To treat symptoms put me on Benadryl. I later went to bed with a body temp of 95.5. Woke up few hours later, wet with a fever break sweat. Noticed aches gone and rash reduced. This was two days ago, aches have not returned. Now on 2nd day, Clariton during day, Benadryl at night. Red rash broken up, into patchy areas and hivey at times. Itchy hot spots occur at different random locations. I am 58 year old white male. Past history of lymes and shingles. Had benign pituitary tumor removed six weeks ago. On Colace stool softner since. Have borderline to low platelid count. Using antibacterial soap for showers (Dial). Have stopped Colace two days ago. Rash seems better - more broken up, but could be the anti-hystemines. Doc thinks aches and rash could be connected. Rash is a symptom of something. Suggestions?