So, you can not get pregnant typically after you ovulate unless you had a very rare occurrence of two eggs in a cycle. This happens like one in 2 million times. But knowing exactly when we ovulate is really sort of rare. You can always ovulate though. It is hard to say in exacts on this subject. If it is 2.5 weeks pat when you had sex, you can take a pregnancy test and should get an accurate result. But please know that all sorts of things throw our period off from stress, anxiety, changes in routine, weight gain or loss, illness, etc.