TMI (no picture) STD's?

Lately my bum hole has been blistered up. Not too major but it's irritated. It started 2 weeks ago. It comes and goes. The only person I have sex with is my boyfriend and we've been together for almost 2 years. He told me he was clean before we even dated. Is this a symptom? Or was it just my underwear or detergent irritating me?