pregnant? advice please

i had unprotected sex two weeks ago (he pulled out, i know this isn’t an effective birth control method), i’m late on my period, constantly feel nauseous, tired, have headaches and get cramps but i’ve taken two different pregnancy tests and they both came out negative? last thursday, when i was due my period i had dark brown discharge and a bit of spotting of blood but that was it, not sure of it could of been just an irregular period or implantation bleeding, any advice please!