Freaking out..advice please

So on the 9th of September a
​My boyfriend and I had unprotected sex and I bought the plan b pill right afterward. The oharmasist said I would probably  see bleeding or spotting about a week later. This is two weeks later and I haven't seen any blood. And my period was supposed to have started on Sunday and still nothing. I am usually irregular. I took two pregnancy tests and they came out negative. Is there a possibility I might be pregnant??