I had unprotected sex on June 1st. My period was due to start June 2nd. It was late. I took a pregnancy test on June 9th with negative results. My period finally started on June 13th, lasting 7 days as usual (in a 28 day cycle). However, it was not as heavy as usual. Still no period as of today, July 18th. It should have began on the 10th. Could I be pregnant or is it more likely that it is just stress?