What to write to my Girlfriend?

my girlfriend hasn't talked over summer vacation, I've tried calling,texting, and emailing her but she wont answer. When school started don't exist.I don't know if we're still together and I really want her back too.I haven't cheated on her or anything like that.We were a great couple.I am also the nicest guy in world cause I am responsible, trustworthy,funny, and caring person. It is hard to move on especially when i have her for four cles and I sit right in front of her for three of them. This hurts even more cause she was my girlfriend and i'm only 15!!! Dammit this sucks to be right now!!! I have even asked her wtf is going on between us but she wont say. what should I do? I haven't talked to her in awhile and its sorta hard for me cause its like asking her out again and I get REALLY nervous when I talk to her now but back then ididn'tt get nervous