When did I ovulate?

I had a peak opk Saturday 30th november late evening but no cramps until Monday 2nd December all day. By su day morning my opk was negative. These cramps on the Monday were as bad as they are when I get first day of AF. Had to use hot water bottle, couldn't sleep, walk etc. Then gone by Tuesday morning but I then had bad diarrhoea all morni g Tuesday. Do you think that was my ovulation? As I surely couldn't have ovulate saturday then implanted Monday. So I'm either 8/9 dpo or 7dpo. AF for three days from 20th November. Last cycle 21 days but that was after having mire a coil removed on 3pth October.