Question about implantation..

If you know exactly when you had implantation bleeding.. Can you count that as the first day instead of the first day of your last period? I had sex on my ovulation days and I was suppose to start on the 22 but I had a small brown colored spot on the 21 and 22nd and still have not had a period. I was just curious because my text have been all negative and if you coins from the first day I spotted it would only be like a week.... Could I only be a week along or does implantation bleeding not matter?