Why do i feel so nauseated?

okay, so i ate lunch, which was like chicken nuggets or whatever from the school, and i felt fine, then by the time the end of 8th period came around i started feeling nauseated like i was going to throw up, so i started freaking out. but the feeling ped. so then we went to advisory, because we were having a prep rally, anyways in advisory i started to feel like i was going to throw up, so i went to the bathroom, and i started gagging but nothing would come up, so i talked to my teacher and she sent me to the nurse. they made me sit near the bathroom for awhile, then my parents couldn't pick me up so i was sent to go watch the prep rally. the vice principal said it would be best if i sat out on the stairs, so that i could get to the bathroom quicker if i needed to. well the feeling was still there. but my face started getting warm, and i kept getting the chills., then i got really tired and almost fell asleep on the stairs. the feeling went away but now it is kinda back. what does it mean? could i be getting sick or is it something i ate? how can i make the feeling go away? please help, we have taks coming up so i can't miss school.