Tips for cumming during sex

Hey everyone, I'm 21 and have had a more than a sexual partners. So far only ONE guy has been able to make me cum (from eating me out) and I've never been able to cum from sex. Nobody else has been able to make me cum from oral sex. It's so frustrating!! I can make myself cum in 2 minutes flat, but nobody else can except my old ex and I don't understand. I can't even make myself cum in front of them and it's so frustrating. Does anyone else have this problem? Or tips?