WTF?!!

I'm 11 days late, got a negative on Day 10, but can't think of ANY other reason to be late! I've never been late like this before (besides my last pregnancy that ended in miscarriage)... I haven't been overly stressed, no diet changes, no exercise changes, nada! Any suggestions?! I'm taking another test in 3 days as suggested by a few IRL friends, just to be sure, and going to the doctor next week but figured maybe you guys have had an experience like this?!