I don't think you have any choice to wait longer. :>) Periods are late and especially around the holidays when stress, changes in routine, etc. all come into play more and are well known for making us irregular. It's too soon to be pregnant from the dec 25 sex--- meaning that is not why you are late now. You will know if that bout of unprotected sex impregnated you in two weeks. Anyway, you can take a test after a full week if you want. But you are probably just late. Always use protection! good luck