What Are The Chances Of Pregnancy After Taking Ipills?

Hello, I just found out that I am pregnant. I had a positive test on October 9th. I was on the pill for the month of August and had a period on September 12th when I began my placebo pills. Is it likely that I conceived in August or September? I did have a period about 2 and a half weeks before I took the placebo pills, though. Could I have been pregnant then and only menstruated due to the pills? Or is it more likely that I conceived when I ovulated in September?