What Causes Discomfort Stomach Along With Early Period?

last month i had my period for only three days then it stopped so the next day i had unprotected sex which made me start bleeding for the rest of that day. ive been feeling really sick to my stomache when i eat and ride in a car which i usually dont do. then this month i started my period on the 15th and im not suppost to start until the 19th of this month. what could this be?