Usually my periods were the normal, 4 or 5 days but in November it lasted 8 days and in December it was 12 days. Is there any reason why its been lasting so long?

There are a number of different things that could be causing your periods to be lasting so long. Your hormones might not be as they should, maybe a thyroid problem or if you have a bad diet(i.e. eating disorders). Or you may have a more serious condition, like polycystic ovarian syndrome. The best thing for you do is to go to your doctor, the gyno, and get it checked out, it is not normal and you should be extremely concerned.