TTC but no luck yet... I think...?

Today would be the last of my expected period.. So.. 6 days late.. I decided to take a test (actually 3) and I'm pretty sure they are negative, I mean it seems pretty clear that they are. I have 2 boys (8 & 5) and ttc but af has stayed pretty normal so far.. Until now. AF should be leaving tomorrow but I have yet to see anything, no spotting, nothing... I have had that feeling like I'm pregnant for last 2 weeks and now it's driving me nuts.. Why are the test clear negative when we've been trying every day AF isn't here?? Should I try another test first thing in the morning? Any advice would be greatly appreciated :)