Last pregnancy I had an implantation bleed at 7dpo (I've had all my BFP's at 8 or 9dpo, so I'm guessing I implant around 6-7dpo each time) , and have always had cramps to accompany implantation.
They however are slightly different from usual AF cramps....they are more like a stretching sensation to the cramp, like things are moving and twisting inside a bit.
Good luck...hope this is it for you xxx