As PPs have said, you probably ovulated later than you think and AF isnt late. How do you know you ovulated? Charting your basil body temperature (BBT) and using OPKs are the best way to really pin point ovulation. You can click on my chart and signup for Fertility Friend. Pretty much everyone uses it to chart their BBTs and it does really help.
Test once a week until AF shows up, you get a BFP or you go 60 days without AF, then call your OB.