Not sure what I'm dealing with exactly but some kind of pe

Ok so my basic symptom is that when I get aroused, my erections are hard and good but I can feel my penis load up with sperm... From this point it takes very little interaction to have a release which rarely feels like an orgasm but more like just a release. I have learned to some what relax and go slow but my girlfriend wants it hard and fast so the second she starts creating a full thrust I'm done... What do I need to do or take to strengthen whatever is not holding the sperm back...