can anyone explain this

i am now cd 31, 14dpo and af is overdue by 3 days.

i did a HPT test on cd 28 and 29 with pregnosis clear and got a faint positive on both occasions. DH was not convinced. So last night CD 30 did another test with clear blue digital and got "not pregnant". tested again ang got negative again.

when i took at the clear blue from the cartridge it shows the control line and another line. does anyone know if this is meant to be the test line? if so shouldnt it have been postitive?

thanks pupa