Why has my girlfriend stopped texting me?

[tikiman14]

Me and my girlfriend have been dating for almost a year. We're both juniors in highschool and last year things were great! we texted all the time and talked during school and hung out on the weekends. As of late she hasn't been anwering my texts or when she does its a one or two word answer and then she'll stop altogether. Almost every weekend I text her and ask her if she wants to hang out and I usually get no response. I really love her and she's said she loved me too but I just don't know anymore. She sits in front of me in one of my classes and doesn't even talk to me usually. If there is time left in class she'll be on her phone on twitter or something and I'm behind her wondering what to do! I don't wanna lose her and I don't know what to do! I'm afraid to ask her because she might get mad or annoyed (if she isn't already). I think about her all the time and I do all I can to see her in the halls but she doesn't seem to be making an effort to see me; I'll go out of my way to pass her in the hall but she doesn't do the same when I know she could. Am I overthinking all of this or should I be concerned?