Ovulation - Did I? Didn't I?

Krissy • Mama to 2 beautiful boys, 1 angel baby and currently pregnant with #3!
In December I ovulated on day 16 of my cycle, in January I ovulated on day 18. Both confirmed by OPK's. It is day 19 of my cycle and I have yet to get a positive OPK.  Is it possible to still ovulate this month? I usually run a 30-33 day cycle.
I recently changed my eating habits, could this have anything to do with late ovulation?