Pregnant or not?

Hi! I just have a quick question... I'm now 5 days overdue, no sign of my period (no symptoms, etc.). Normally, my period is at most 2 days late. I've taken several tests (cheap and expensive), but they're all negative. To keep myself from going completely crazy, I'm testing about every other day, but I was wondering if anyone else has experienced this? I don't really have any specific pregnancy symptoms, but I do have a near-constant cramping/pressure (?) in my lower abdomen.