When to test?

Mallory

I have irregular periods so I'm not sure when AF is going to show, I had a positive opk on 12/31. I'm having cramping and pinching feelings on the left part of my uterus (which I never get before AF) that is off an on for the last 2 days and cramping stronger at times which this I thought was AF, and nothing so far. If this is implantation, when would you recommend me testing? TIA!