Pregnant????

Me and my boyfriend had unprotected sex on night after he got home from drinking with his buddies. We he did the deed inside me and the next day we got a plan b pill. I have never taken one of these. The night we had sex was after my period. Well the next two days after the plan b pill I had another 5 day period. It has been a month and 3 days now and I haven't had my period yet. My cycle is usually 28 days and 4 days of bleeding. I am never late. Could the plan b pill have pushed my period a week behind? Or could the plan b pill have not worked at all? Is there a chance I could be pregnant?