Whats wrong with me? I never get hard or...

Whats wrong with me? I never get hard or turned on without something touching my penis. Ill be making out with my girlfriend, naked, rubbing her tits and vagina, and i won't get hard. All my friends said they get hard after kissing for a little bit or when the girl takes off her bra and they hold eachother. The only time i get hard when im making out is if my girlfriend grinds her hips into me, and even then i don't get all the way hard or it goes limp after a few seconds. It works fine after its hard, but it ruins the moment if i have to play with myself or my girlfriend has to work it up. Any information would be greatly appretiated, even if its just "i get hard hugging my girlfriend or grabbing her ass."