You ovulated late. If you had ovulated on time, you'd have gotten a period or a positive test by now.
If you are testing negative, you are not pregnant at this time. Since ovulation happened later than you thought, that means you could also easily be testing too early. Test again about once a week until it's been at least three weeks since sex (unless of course you get a period).
Also, be sure to use a regular, generic test. No high priced name brands, and definitely no early detection tests (which are highly prone to false negatives). The highest rated tests are generic, specifically 99 cent store tests.