Irregular periods

I came off of birth control pills 2 months ago. Last months period was a 32 day cycle and this month is a 28 day cycle. I was surprised to get it early. I was thinking it was implantation bleeding. How do I calculate when I ovulate for this month. Last cycle I bled for 3 days and the last 2 days it was very little blood with discharge. Would I count those last 2 days as part of my period. Just trying to figure when my fertile window would be this cycle.