question. not sure where else to ask..

may be a bit confusing.. asking bcuz we think im further then they say.. going back to sept/Oct. I'm had a normal period in august... my fertile week in sept was the 6th-11th. we had sex on the 4th, 7th, 9th and 15th. On the 23rd i got my "period". it was not normal at all... was extremely light and only lasted 3.5 days.... got impatient and took a home pregnancy test on the 19th of Oct and got a very fast dark positive. purchased a digital to see how many weeks and it said 2-3 weeks... going by the paperwork that it comes with 2-3weeks actually means 4-5weeks..... so was the "period" i had in sept actually implantation bleeding???? cause that is the date i gave to the dr for my last period... should i have used my aug period instead?