Pennis length is too short

Patient: Hi Doctor. I am 26 years of age. Average body. Social smoker and drinker. My problem is that, my pennis is too short. When erected also, its only 3.5inches and which is making me uncomfortable. And also, few weeks back, i happened to have sex with my girlfriend. I am not able to do sex. Even before 2 mins and also during foreplay, i gets cumming(Sorry I dont know actual word. Hope you understood). I am totally desperate on these things. Kindly suggest me whether there is any hance of increasing my pennis length and the sex duration. Waiting for your reply at the earliest.