Suggest Treatment For Blister On Penile Shaft After Having Sex

I have a blister on the shaft of my penis immediately after sex I am 25, 5 foot 10 weighing around 13 stone I exercise regularly around 5 times a week mainly weightlifting and some cardio work, after sex this morning I got a blister on the shaft of my penis immediately after finishing , this has happened twice before but goes away after a couple of days and isn't itchy