I'm on apri the birth control pill. i've taken many pregnancy tests it's been 42 days since sex. can my birth control make the tests negative?

Yes, indirectly...: Birth control will "cause" a negative pregnancy test, which is a main purpose of birth control pills... they prevent pregnancy, thus causing a negative pregnancy test (because the woman is not pregnant). However, no contraceptive is perfect, so if a woman gets pregnant while on birth control pills, her preg. test will be just as POSITIVE regardless of whether she is on or off birth control pills.