How long after implantation bleeding can you tell if that you are pregnant?

I spotted last month I thought, the month before that I didn't have a period and then this month I haven't had a period. I know that I could have other problems, I've already been to the doctor and that is getting me no where. So does anyone know how long it takes after implantation to know that you are pregnant? I don't want to get a pregnancy test to soon.