Sharp Pain on 4th day

[Monkeybrain]

Hi I'm a 32 year old woman , I've had phases of diffcult periods, with pain on second day, and heavy bleeding, and phases of irregular periods.
But as I'm quite active and work out a lot, these issues would resolve themselves and I would have painless "normal" periods . Over the last few months my periods were very light, lighter than usual. But after 3 months , I had a heavy period, with clots and everything, the strangest thing was , I didn't have pain on the heavy bleeding days, nor on the first day. But on the 4th day I had the sharpest , crippling pain. I'm very confused . There have been some days where I've felt similar pain before passing out a clot, but never on the 4th day.
What could it be?? It's close the end of my period and I'm getting such an intense pain like it's the first day. Any ideas?

[Monkeybrain]

It's the 5th day and the pain continues. I just don't understand. Why is it acting backwards. My period is supposed to end.