How long after giving birth will a pregnancy test continue to show positive?

Mother Isis asked:


I have a baby boy that is nearly 4 months old. I did have a period last month, January 18th start date. I missed this month and was about to go ahead and start birth control, but thought better take a pregnancy test to be sure. They have all come back positive.

So, I am just curious if I could get a false positive after giving birth back in November of 2008.