vomiting,dizziness,short of breath, missed period, always ti

Hi there:
I have been having very bad stomach pains, such as multiple swords just stabbing to get out. As I am in school, im getting really dizzy. Im always tired and never am myself, because all i want to do is sleep. I vomit alot, especially after my meals, but i usually only eat something small, because my stomache really hhurts. Im on a swim team, and when i only swim like 25 m, i am outa breath, and cant swim. I dont just get short breath swimming, i get short breath everywhere, if i walk a few, i loose my breath. i havent had my period for 2 months now, and im getting told im pregnat, but that cant be true, i havent had sex. recently i have had these awful headaches, and bad chest pains.

any help?