Repost od Not Sure

I'm 24 just gave birth 2 months ago on June 11th. Doc. said ok to go back to normal activity and started birth control. Had sex on July 11th then had lot of red blood on the 16th then nothing and sex on 17 then again nothing. Had period from the 19th till 24th. Had sex again on the 25 then nothing. Then spotting on the 29, 30, and 31 stopped birth control after spotting happened. Not on birth control any more. I am now a day late on my period. Could I get pregnant already, is it just my body getting back to normal, or could the birth control not worked right away? I also lost over 70lbs being pregnant, but ate all the time.