Are these blisters painful?
I put neosporin on them after my shower. They do not itch, and are not very painful. I am not sure if they are ulcer formation, but at this point they are very shallow and seem like they formed only at the very top layer of my skin.
Usually herpes present in a crop of blisters as you describe and there can be associated systemic symptoms like fever,fatigue,lymphnode enlargement as well.
So chances of herpes can be there in your case.
Also they spread from direct skin to skin contact from infected person.
Having said this you should be seen at a GUM clinic to rule out other STD as well since you have a history of unprotected sex as well.