I've been masturbating to porn too much till a point where i find stimulation from a girl's touch less pleasurable to cause an erection.

Ur still growing up: You're young and still learning about and practicing with your body. When you're by yourself, it's important to vary your grip and technique or you may be less responsive to particular partners. Today's images create unrealistic expectations. And casual sex is always disappointing long-run. When you are excited about who the girl is, and love her for her qualities, you'll be a more complete man.

Reduce porn time: Things will normalize if you reduce your exposure to self-gratification--your body will prefer a partner. And remember to use condoms.