OP I've been doing the exact same thing for nearly 7 months now(Nearly daily), no problems what so ever. Don't fuck her again till you've pissed after you came though, the sperm left behind in your dick will get carried into her vag by the pre-cum, which you do have.
You know you don't really feel the precum right? How would you know if you're precumming? Which leads me to my next hypothosis: You could get her pregnant.
Why dont you just get your girlfriend to use some kind of contraception? My girlfriend had the injection (she says the pill makes girls fat). Unprotected sex is so much better, but it's not worth ending your whole life just for a little bit extra pleasure.
The pill isn't right for everyone. But there's also the shot (like you mentioned), IUD's, regular condoms, female condoms/diaphragms... The pull-out method and the rhythm method are the ones we were all taught don't work. And I love how everyone who uses those methods always says "well, we've been having sex for X amount of time and she hasn't gotten pregnant!" ...yet. You've just been lucky so far.
jesus man, read a book. NO-ONE has the ability to stop tiny amounts of "pre-cum" or cum from coming out during sex. The pulling out method is as effective as the "do it standing up" method. or the "make sure she showers afterwards" method. all total fallacy. I wont even get started on the diseases you could open yourself up to if ine of you is unfaithful or already infected with anything. Sorry if i seem harsh but you are gonna end up a daddy and you are definitley NOT ready for that.
1. Pullout method isn't reliable. 2. It doesn't matter if you urinate or not, but holding semen back sometimes gets semen in your liver. Drink water and you should survive.