How to start birth control pills

I gave birth 1/7/22 I saw my obgyn and she sent my progestin birth control pills to the pharmacy. I didn’t have any questions until now that I’m looking at the pills. The pills are labeled Sunday-Saturday. I called the pharmacy and they said I’m supposed to wait and take them until the first Sunday after my period. But that doesn’t make any sense because I read it can take 6-12 weeks after birth to get you’re period. I doubt I’m supposed to wait until my period to start. So when do I start taking the pills?