I am a 26 year old. This is embarrassing but my g/f and I have sex a lot and for the past 3 times I have been going limp. I don't know what's going on its new to me and am very worried. I don't know what to do. I don't masterbate to porn or anything because I have her. I have no problem getting hard just when we get intimate it goes limp after a while. Please help