How Many DPO Am I?

I got a positive opk on CD 18, March 26. I got up March 27, CD19, and tested and my opk was negative. But later that morning I had the most painful cramping in my left pelvic area. The pain was so intense I vomited several times. After a couple hours the pain was gone and I felt good as new. My question is, when did I ovulate? Did I ovulate at CD18 when my opk was positive or CD19 when I encountered that horrible pain? I'm curious because Glow says today I am 4 DPO which means Glow says I ovulated on CD19. But could I be 5 DPO?