I ovulated on saturday night, and my period started yesterday (thursday) so i got my period 5 days post ovulation. why would this happen?

Short luteal phase: the luteal phase is the time from ovulation to the onset of your menses and average is 12-16 days. your recent cycle was short. the ovary produced low progesterone during that cycle. there are many causes for this and if you monitor your cycle and find that there is a consistent pattern, I recommend that you consult your gynecologist.