Anybody can be late at any time. It happens. You had protected sex (good) and he didn't ejaculate (good). This certainly brings the odds WAY down. And you took pregnancy tests that were negative. You will most certainly get a positive test if you take a pregnancy test 2.5 weeks after the intercourse you are worried about. We can be late for the following reasons such as changes in routine, stress, weight gain or loss, illness or blips in hormones. Your period is likely on its way. If it goes past two months over due, consult with your doctor. But even then, it can be normal. Just really a long cycle.