i had unprotected sex with my fiance a week before my period starts

I've been celebate for 8 months. i had unprotected sex with my fiance a week before my period starts . I've been nauseous ever since, my lower back hurts, i get very tired. My period came a day late but i wasn't feeling bad cramps like i used to before, it's very mild. I keep feeling hot then cold,every time i belch it taste like vomit...could I be pregnant?