i feel like i'm dying!

before any one thinks, i am NOT pregnant. never got intimate. but i feel nausea all the time. i get head aches a lot and i feel like my brain isn't functioning and i'm tired a lot and i feel lousy. i have a disease, Ulseritivecolitus.. i don't think it's from this. i'm 14 and i don't know if this is normal for my age.. please help.