-I agree w/ smjmekg. A HPT will be reasonable accurate about 14 days after possible conception (you do not need to wait until you miss a period to test if you have an idea of when you had unprotected intercourse)
You could be pregnant if you have had unprotected sex, women ovulate at different times in their cycle and it is possible you ovulated earlier or later.
no in a normal 28 day cycle you wouldn't ovulate till may 13th. You probably just got sick.