Cramping?

So...I am about 13 dpo. I started bleeding last night, day 26 in my cycle. For the all but one of the previous five cycles I have had my af at day 24 or earlier. Last month had a cp and had my period at day 28.  So I would normally think this was my af just a bit late but...when I had the cp I had implantation bleeding. And this time I have cramps and I NEVER have cramps. Had taken tests last two days before I bled and they were BFN. Anyone have any insight?