Not to be Debbie Downer, because there's a good chance it IS impl. if it's a new sensation, but I've had many times now where I have felt what you're describing and then end up having an AF visit. I've driven myself crazy with hope and now TRY to ignore anything except a late AF (easier said then done sometimes, right?).
I really really hope it is implantation for you all!!! Update us when you find out, please?