Ipill and menstrual cycle. Menses) ?

Hello, I am married and has a child of 1 and half years. Due to unprotected sex, I had to take i pill in the month of august and september. Periods were regular until september. But in september I had menses only for 3 days which was usually lasting upto 5-6 days. But unfortunately in the month of october, I did not get my periods. (Menstrual date was supposed to be on 24th). So I did a pregnancy test and is NEGATIVE. Is this delay of menses is effect of i pill? If so, when can I expect my periods? Also, are there any chances of getting pregnant if done unprotected sex before the next periods? (I mean, are there any possibilities of ovulation without menses)? I humbly request you to give me answers for the listed questions. Thank you.