Hie Iam A 27 Year Old Man. I Noticed Some

Hie Iam a 27 year old man. I noticed some sores and blisters on my penis about 3 months ago. It was after I had unprotected sex with my g/friend. The sores and blisters seem to appear and disappear in a period of 2-3 weeks since they started to show up. I do masturbate since my g/friend lives far away and we can only meet after a period of 2 or more months.What might be the problem?