Could I be pregnant again?

So I’m 6 month postpartum and I just got my first period after giving birth last month, March 27-April 1st. My fiancé and I had unprotected sex on Saturday April 21st. I took the plan B pill Aftera, the next day. I was supposed to start my period on Tuesday the 24th. It is now almost a week past that and still nothing. I get slight cramps and back aches and I feel nauseous all the time. That’s also a side effect of the pill though. I was wondering if anyone else that just had a baby had this happen to them? I was told you’re very fertile after giving birth but the pill is supposed to be 95%-90% effective the first 48 hours. I know it was stupid of me to let this happen and I’m worried I will get pregnant again and not have enough time or energy to watch my first born grow up. Anything helps! Thank you