Could I be pregnant?

Well to start things I do have 2 children already. So I'm no stranger, but I'm baffled. With both of my children I tested at about the 3-4 week mark and showed positive before the tests were even completed.

I should have gotten my period on Nov. 24 but it hasn't come yet. Over the last 2 weeks I've taken 4 or 5 pregnancy tests and all are negative. I want to get opinions before I make an apt with my obgyn for a blood test.