When did I get pregnant

In October my period started October 8 and ended the 12. Usually my period is 7-8 days so this was a very short period. Anyways I took a pregnancy test Wednesday Nov 1st. It was a dollar test and it was bright red positive almost instantly. I took 3 clear blues after that all instantly positive. To me it seems to early tk have gotten postives... I got a positive exactly 3 weeks after my "supposed" period ended... could i possibly have gotten pregnant last month?