I'd like some help to a problem I'm having. Sometimes when I'm having sex with my girlfriend I will just lose my erection. This can be during a pull out and when I'm inside of her but when it happens I lose it for a while sometimes to the point that we have to stop having sex cause I can't get it back up. I haven't ejaculated and I don't know what's going on. I'm 18 years old and a college student so I'm kind of doubting it's a health problem and I'm not stressed or tired. I'm an athletic guy being a martial artist. I know it's not me having a problem with the girl cause I'm crazy for her. But this can be so frustrating cause I just want to please her. Another issue that I have is that sometimes my penis size varies and I don't know why. During masturbation, I max at 7" but when I'm with my girl I reach 8.5" to 9" and I can notice a difference in the feeling between the two. The thing that is also noticeable besides the change in length is also a change in girth, mainly the girth of the head of m penis. When I'm closer to 7" my penis head tends to be pretty large while when I'm closer to 9" the head of my penis is smaller. All these things about my penis I'm confused about and I'm hoping that some people on LPSG can help me out to understand my body more. Thanks to anyone who provides me with some help.