Short Period and Ovulation

My IUD came out the beginning of Jan this year. With it my period didn't exist. That month I got a 7 day period. The next 2 months were 5 days, the following months were 3 days, and last month it lasted 2 days. It has been blatantly obvious when I ovulate. This month (after my 2 day period) I haven't done the "obvious" ovulation. I only have 2 days left for this ovulation and I'm a little lost. Do our bodies sometimes skip it? I'm not worried, but curious. My signs are always the same. My nipples will have the sharp pain (the kind you feel inside your boob) and I'll have more then enough cervical mucus. This time I got a slight pain in one boob for about 5 minutes and that was it. It happened at the beginning of my ovulation timeframe. That's been the only symptom. Anywho... Just curious. Any thoughts?