I am in a similar situation, i had unprotected sex with someone last year and started being sick (having itchy rash on my face every months for 4 to 14 days, ive met about 8 generalist, 1 alergologist, 2 dermatologist and none of them can tell me what it is, i took the std test and everything is negative). i would say its not impossible that what you have got is actualy contagious without being a std, yo