If your period was abnormally light, then you might want to take a pregnancy
test just to make sure.
It is not uncommon for there to be some fluctuation
in a woman's cycle from time to time. Stress, diet, weight changes, and hormone level fluctuation are some of the causes of this irregularity.
Ovulation usually occurs at the mid point of a woman's cycle, somewhere between 12-16 days after the start of her last period. I would recommend you keep track of your cycle.