bleeding during sex

Whenever I’ve had sex I always bled. I talked to my doctor and they said it’s probably just because I’m not lubricated enough. It’s always super embarrassing and makes it hard for me to get intimate with my partner even though I really want to. Last night I had sex with my partner for the first time and I had told him ahead of time sometimes I bleed. We had bought lube and used a good amount of it. When we were done I had apparently bled and it was mortifying. It wasn’t as much blood as I’ve had before in the past but it still was enough to make me die inside. Luckily he was really sweet and just wanted to make sure I was okay and I wasn’t hurting. I’m free of STD’s and all that and it doesn’t hurt while I’m having sex. I really wish I could just figure out why this happens. I can’t see a gynecologist because Im a college student who lives at home and my mom is very traditional. If anyone could provide any tips on how to avoid this or any advice that would be great. Thank you! :))