Stop watching porn.
Seriously. It gives your sexual mind unrealistic expectations, and it accustoms you to your own hand more than another person's flesh. Ever wondered why a lot of porn videos have the guys finish themselves off? Half the time they barely feel anything to their "partner" and thus have to stimulate themselves.
I can attest to this personally, too. A few times I had the ol' Whisky Dick despite being incredibly into the girl. I blamed the school stress and alcoholism, which are legitimate problems, but then I got to thinking that all the porn probably isn't good either. Seeing boobs, ANY boobs, used to be a big turnon, but if you're seeing naked D cups everywhere, it'll lose its allure.
Porn is bad. Not morally bad (at least not in this discussion) but bad in the way that McDonald's is bad. Cheap, quick, easy fix for your hunger, but over time it does more harm inside than good.
Give up the porn, go do more cardio and do more lifting, oh, and get rid of sugary drinks. The sugary drinks may not play a role but it's just general good advice. Especially as drinking water and high-citrus juice (unsweetened Pineapple, for example) will make you taste better.
Go do it. In a month of no porn and no masturbation, you'll feel like a 16 year old again.