Late period, Negative tests, Not stressed

Marissa
So, fiancé and I don't use condoms, I'm not on birth control, really we just don't use any protection. 
My period is now 2 weeks late with no signs of showing up any time soon.
I took one test 1 week late and I took the second one this morning, both turned up negative.
Nothing out of the ordinary is occurring in my life right now. Can anyone explain?