Well, with any pregnancy your doctor will be able to confirm how far along you are with a blood test (a lot more accurate at determining the HCG in your system too)
But, with a HPT you normally don't get a positive until about the third week or so of your pregnancy. So I would guess that you are about a Month a long, maybe a bit longer if there are other factors involved.
Definitely make an appointment with your gyno to make sure!
Good luck and Congrats! :)
when was ur period in september?
Approx two weeks prior to your positive test give or take a few days.