What Causes Blisters On The Penis?

Can I get blisters from masterbating. This is the second accurance this month. I'm 28. I've onlt had sex with two people in my life. One when I was 16. And then didn't have sex again till 25 and I'm marraid now to that person and have been for 3yrs now. I fear it could be.herpes at times. But then I don't know where I would have gotten it.I'm worried and don't know what to do. The blisters this time are on tge head of my penis right where the head and shady meet. There are 3 of them. They don't itch our hurt.any clues what it could be. I do masturbate alot. And have sex with my wife atleast once a day too