Certain rashes are caused by STI (sexualy transmitted infections ) . You should go to a hospital and get tested. If you can't afford big hospital bills you can go to a Tena tabiya card only costs 2 birr and the tests they give you are very cheep if they have them there. Please get checked for syphilis and the rest of very common STIs . Don't wait too long if you have contracted something the more you wait the more the worse the outcome.