I m afraid if i m pregnant?

Help me people please. I had unprotected with my boy friend on the seventh day of my cycle. And now its been a week since its done. After that we never hav unprotected . Now im afraid if i will get pregnant or not. I have 28 days cycle. Des days i m having alot of problem with my health. Having gastric problem which is making me difficult.. after food my stomach is paining badly. Today.. after my food i felt like vomiting. Wen i went to bathroom and vomited. it was just a little saliva mixed with water. I am really scared... Please tell me ... what all to eat to prevent pregnancy... I m having papaya... Is it that i have to eat... ripe papaya .. plz help