implantation?

Destynee • PCOS • 2 natural born • pregnant with our letrozole baby🤍
My cycles are irregular and when they are somewhat normal they last around 35 days. I'm currently on CD 28 and 7 DPO. I've been cramping pretty bad since yesterday and today! Could this possibly be implantation? I can't really say what normal is for me, but I don't feel like this is normal at all. Especially since my cycles last into the high 30's. I got a very positive OPK on CD 21 and I've never had one so postive and dark! So I'm hoping I caught my window this time!!