Hyper urination before sex?

I'm 17 and have been having sex with my girlfriend for about a year now. Every time we are making out prior to sex, I have to pee like 2 or three times. I feel like every time its practically a full bladder of urine, so its not like i get a hyperactive bladder- more like a hyperactive urinary system. Its a hassle to refrain from consuming liquid fro several hours beforehand, and it sucks to have to constantly get up and pee while we're going at it. If I ignore it, its uncomfortable and she can tell I'm not really enjoying it. Addtitionally, I dont have to pee when im horny, just when we're naked. I thought at first it was just because I was nervous, but now that I'm really comfortable I'm thinking its something else. What should I do??? Why does this happen??? I don't want to hear "go see a doctor"... any good guesses?