What Causes Delay In Menstruation Other Than Pregnancy?

My boyfriend and I had unprotected sex on october 28th,I didn't let him "finish" inside although I know there is still the chance of pregnancy. I went to the doctors november tenth to get prescribed birth control and they did an hpt urine test which came back negative. I started my period on the 12th and started my bith control on the 17th. My period was shorter but not lighter. For the last week my nipples have been really sore and increasing daily, although my period was just a week and a half ago. I've also been exhausted but I was blaiming it on my crazy schedule. Could I be pregnant even though the hpt test came back negative or is this just the birth control messing with my hormones..