My last period i had in the last week of november it last alil til december had sex a week or two before december endedbut it was half fast a for a mi?

Hard to understand: your abbreviations. It may be a simple fluctuation in your hormonal cycle. Many factors can cause hormone fluctuations, including weather, exercise, nutrition (or lack of), emotional distress or stress, illnesses, big changes in routine, and infections. And sometimes waiting things out to normalize is the proper approach. However I would check a pregnancy test and repeat in 1 week if neg.