penis pain

back when I was dating a very pretty lady, she wanted sex 3 to 5 times a week, but I learned that after the fourth or fifth time, that even though she was on the pill. When I was inside of her, and I came, with in about 10 seconds of my last shot, the end of my penis would be very painful like getting stung by a bee. When I pulled out the tip of my penis would be very sore and swollen. I would need to clean and was really well after. I was tested for STD's and I was clean, thought it might be a sperm aside, but after putting on a rain coat I was fine.

Never had that problem again, anyone else ever had anything like this and know why?