Hi If I Had Unprotected Sex Last Month Of 2015

Hi if i had unprotected sex last month of 2015 September 8, 9, 18, my last period was September 12, 2015 my expected period was supposed to start October 10, it didn't soo.. i went and bought a pregnancy test and it showed up postive today October 12, i starting bleeding red heavy could it possibly be implation bleeding ? is there a possibility that i could still be pregnant ?