I get this red blotchy hive/rash on my chest and neck when I am extremely nervous, excited, hot and also after sex. Please help?

Cholinergic urticari. This is known as cholinergic urticaria arising during the cooling phase after a rise in core body temperature. You may try taking an antihistamine about 2 hrs prior to sex or exercise in the future. Avoid Benadryl (diphenhydramine) if you plan to have sex but the other ahs are usually ok.