Why do I feel this way?

I feel sick. Not feverish. Not like I'm about throw up. But just sick. I feel lost, empty, like I have no purpose. I am 13. I have stayed home from school two days in a row now. I have this pit in my stomach. I feel like I want to cry, actually I'm crying right now. I feel like I want to scream as loud as I can. But the thing is, I have no REAL reason to. Nothing that bad is going on in my life. And I'm scared about the way I'm acting.