What Causes Painful Blisters On Penis Tip?

am 26 years man weighing 73 kg with a height of 163cm. am healthy never faced such a problem before.i developed painfull blisters on the tips of my penis, a had an unprotected sexual contact three days ago. I still remember when i was having sex on that day i almost creamed because it was so painfull what could it be. Please help meohn