Its hard to talk to girls (guys & girls)?

when i was young i guess, my brain didn't develop all the way to think about girls and anxiety about them and think SO much about girls. I use to e able to talk to any girl and flirt with them. Now im 16 and its impossible i think girls are judging me all the time. Evey time im next to a girl my mind thinks "am i being weired is she looking at me". Does she think im strange all these questions stumble me and i look so Wired in front of her but i think most of it is in my head. I cant even look at her sometimes and shes over there being completely normal unlike me but i can tell shes nervous around me is it because im making her nervous?! what could be the reason