My husband and I had unprotected sex once and I took plan b an hour later. I got my period a week later, but it was light and lasted 4 days when mine usually lasts a week. This month I waited and did not get it at all and this is the last day of the month. I took a pregnancy test last month even after I got my period and it read "not pregnant" I have not taken one since and me and my husband are very confused. Is there a chance I could be pregnant even after getting my period last month?