could i be pregnant, please help

last week i threw up bright yellow without feeling sick, i just threw up out of nowhere. 
ever since then i've been having stomach pain at the middle of my stomach, again i don't feel nauseous or anything. but today i had a fever, headache, & i feel nauseous. i got off my period jan 1, it was really heavy. & last week i had unprotected sex using the withdrawal method on jan 2&6 and nov 20 before my period. could i be pregnant?