My Husband Has Been Hearing Two Heart Beats In My

My husband has been hearing two heart beats in my stomach for the past four days... I got my period 3 days late and it's a lot heavier than usual. I've been getting very nauseous and bad stomach pains. I've gained a little over 5 lbs in a week and I have been eating more than usual and strangely craving watermelon. My husband and I have been having sex every day for the past month. Am I pregnant??? If not, what's wrong with me???