i am 18 years old and have been in a relationship for a year. We do have unprotected sex but have never fallen pregnant, my period has always been on time which is the 25th of every month, on the same date and last 3-4 days max, except december i came on normal time and was on for 9 days which was very unusual, we have sex regulary but have never caused a problem, in january i came on the 10th and i assumed i would come on again this time again but i havnt,why is this???