Hello respected, I think you are experiencing urticarial wheals, a type of allergy, matches your description, usually very itchy, but in few cases gives just feel of warmth. The reason in your case is most likely autoimmune type of urticaria, commonly associated with autoimmune thyroid dysfunction. You start taking antihistamines like levocetrizine 10mg at night time, duration of treatment we can t guess, some may get relief in few days, and some may have to take the drug for few months. and if no response or condition continues than immunomodulater drugs like steroid, cyclosporin, azathioprine may be required. another reason of rash in your case may be drug induced urticaria.so just observe the time of onset of rash, and also get done thyroid auto antibodie profile, -TPO antibody -anti TSH receptor antibody -anti Tg antibody