What Could The Big, Painful White Blisters On My Left Testicle Be?

I Want to know what i have, on last saturday i had sexual relationships with somebody i dont know then on monday i got a little blister on my left testicle then on tuesday i got more, they are not in groups just by themselve, they are big and white and they hurt but not too much, but when they explode the skin becomes red,also everything is just on the left side and i dont have any on my penis, i am going to send pictures, please tell me what could it be.