Late Period vs Pregnancy

About how long after pregnancy does it take for periods to become regular again? I ask because I had my baby on October 16th and since then I've had two periods, one on November 29 and the other December 29. If I go by the length of that cycle (30 days), I'd be exactly four days late. However, before pregnancy my cycles were 30-32 days and if I go by 32 days, I'd be two days late. I know, I know.... I should pee on my phone to see if I'm pregnant, but I don't want to jump the gun and start freaking out when it's normal for periods to be all over the place after pregnancy.