I have been having regular periods for awhile now. Usually starting between the 4th & 6th or each month. Well last month I started the 14th just about a week late but I still had a period.. but this month I have yet to get a period & yes I have been sexually active, Could you please tell me why this could be or what is the problem?

This could be a number of things... first off you need to do a pregnancy test. You should see your OB doctor or family doctor. It doesn't say how old you are but you should have a pap done to check for any abnormalities. Also stress can screw with your body as well and sometimes can mix up the cycle.