Waht Could Headache With Nausea And Sore Breast Suggest?

Over the last week I've had severe headaches, I just ended my period on Sunday. Now the last three days I've had stomach pains,but today it's really bad, I feel nauseous, I have diarrhea and my breasts feel sore. What could be causing this? Is it possible I'm pregnant? Last time I had intercourse was on Sunday.