Why the hell cant i talk to girls?

ok first off i dont want to hear: "beauty is in the eye of the beholder" "your young" "havent found the right one" or any of that crap. ok to get a general idea of me: im 17, 6'2, 170, and white. im decent looking and dress sorta skater esque. also, ive had intimate relationships in the past and have hooked up. BUT I STILL SUCK AT TALKING TO GIRLS! i always have but its getting worse. i get nervous and cant even start a conversation. i can barely look them in the eyes and i come across as an awkward moron. whats worse is that i always thinkof something clever and flirtatious to say after the fact! it pisses me off so bad cuz i know im not ugly and damm if working out hasnt given me a nice body too. physically im very confident but i cant effin talk to girls. especially hot ones.