I get cramping starting around the same time. When I was younger, it started later (around 12dpo), but it got progressively earlier as I got older. I suspect it's related to my endo (because of the progression), but that's a separate issue. When I was pg with DD I had all my normal LP cramping and it continued all the way through to 15wks... For most of the 1st tri I felt like AF was about to start any minute and it drove me batty some days! I also had cramping during the LP with my other 2 pgs.

You say you've been pg 7 times, but have any of those been since you started getting this cramping? Maybe you will have cramping with your next BFP?