Why am not pregnant?

Patient: So me and my bf had unprotected sex 11/24/2013 he nutted in me that was 5 days before my ovulation began then we had unprotected sex 12/05/2013 that was 5 days after I ovulated ,I keep having periods Im trying to figure out why am I not pregnant im gaining weight I took 2 pregnancy test 1 negative 1 positive please help me