IDK how long it takes to go back -... the first + day is your + OPK. I have always stopped taking OPKs after that. You really need to chart to confirm when your O date is but you should O anywhere between 12 - 36 hours AFTER your + OPK, which in your case was on the 14th. So you've probably already Oed. Really though to confirm O, your temps rise. Check out
Taking Charge of Your Fertility by Toni Weschler for all the details on charting.
The 2 MOST fertile days are the day of your + OPK & the day after so sounds like you are probably covered to me so I'd stop if you haven't already.

But like I said to really confirm it chart & when you get 3 days of a temp rise you KNOW you Oed & that's when I stop.
I don't have cramping anymore myself... if you are still actively cramping maybe you didn't O after all but it could be that you're not cramping at all & maybe the cyst has formed & it is just tender when you move a certain way or whatnot... I know that is the case for me anyway.