Anyone have any suggestions? Please Help me!!!!!! What to do?

There is this girl I've known for 2 and half years and I don't know why, but she doesn't talk to me that much. You use to talk to me a lot, but she has been acting wierd. I'm a intelligent and not a y guy. We're both in 9th grade. The problem is that I'm a shy guy around her and I don't have a high amount of confidence. Also, I have sometimes very low self-esteem. I think she might like another guy and I have been getting heartaches on what to do. I feel like I should either quit our friendship or ask her out. I don't know what to do? What should I do? Please Help!!!! Thank you for people who respond to this question. Finally, please no stupid or dumb replys to this question.