Advice Please!

On the 31st of December 2016, I was four days late for my period. I have always been like clockwork with my cycle (even after having my first little boy) so naturally I got excited and went and bought a few tests. They all came back negative and the next day I got my period but it only went for four days which is once again very odd. I didn't bother to take any further pregnancy tests after this. I am now currently three days late for this month and am wondering if I should be concerned because my cycle is out of whack which is abnormal for me. OR should I be getting another test?! There is no obvious reason that would be causing my cycle to be irregular either. Sooo ODD! Any advice would be greatly appreciated!!