T.M.
You could go a year or longer with out a period, depending on how long you breast feed. Breastfeeding is a form of birth control in it's self but it's not 100%. I would wait for other symptoms before rushing out for a pregnancy test. Or if you think you may have concieved on the 2nd, then if you still think you are go buy a test (at the Dollar Store) on January 2nd. You'd be four weeks by that time and would have already missed a period (if you were to have one.)