I can remember having those feelings when I was at home and in school, I dont know what to tell you as to how can you tell, it sounds to me like depression or the early stages.I think if you have family doctor or even if you dont that you could ask to see a doctor and just explain to him or her what you've told us here. I am in no way an expert but seems like it can only help to talk about it, feel free to pm me and I will listen, and do my best to give you advice but my first peice of advice is to if you cant talk to your parents talk to a counciler at school or church. I dont know how your situation is so its hard for me to say but i think you should talk to someone. and I am very glad you shared your story somewhat here. its good for you and can only help. People care and they care alot about whats going on in your life.
Pm me if you need to and I can give you my email and we can talk all you want.

Tonya (Brokenwing) my indian name