My period is 5 days late n negative hpt!

My period is 5 days just took a home pregnancy test (hpt) and its negative how could that be?
my boobs hurt i feel nausea in the am im tired i got off birth control pills november/december just had unprotected sex feb 9th my fertile week was feb 10th till feb 15th.
i think i had implantation bleeding on feb 20th i spotted once that day 
could i be testing too early?