I get an erection every 20 minutes, seen my doctor they said nothing was wrong and my girlfriend gave me a prostate exam using latex gloves (felt good?

Good for you. Enjoy being young. This is well within normal limits for a teen. This is a time for exploring and learning about love -- and especially to love responsibly.
Teens and Sex. First, this time will pass. It can be frustrating to have an erection all of the time and all boys have to deal with this period in some ways. Yes, the prostate is full of nerve endings and many men learn to enjoy some massage of this during their sexual play. Many girls learn that this is a special secret to please their men and enhance their orgasm. This is normal, and common.