trouble in bed

im 18 years old and im having some troubles in bed. So let me preface this by saying i have jerked off to porn or (probably more commonly) to pictures of girls at minimum once a day and alot of the time more for probably the last 4 years. About 6 months ago when i had the first opportunity to lose my virginity i was in bed making out with this girl and i couldnt get hard. Not at all. I left this down to first time nerves or whatever, fast forward a month and i got a girlfriend that im with right now. We have had sex alot of times probably 15+ but never once have i came and im having trouble staying hard. I get somewhat hard cuddling with her and whatnot and when shes using her hand its alright, but i can just never seem to keep it up for the full session. At first i would get hard and then when trying to put it in i would just go soft an have to back out. This is insanely embarrassing and a total mood killer. Quite a few times i have been hard enough to get it in but not super rock hard, and after going for a while and i pull it out i realise ive went almost completely soft. For me it seems getting off with her vagina is very difficult and ive only came close to cumming a few times.(we tend to use alot of lube so im not sure if thats killing the sensation?) I have no idea what the problem is, I know i am attracted to this girl. I can jerk off to pictures of her easily and i find her very attractive. But in bed i just cant seem to get it done. I know its not down to nerves because im very comfortable with her so what else could it be? any help please because this is making me super deppressed. Why cant i be normal?