Anyone good with insurance knowledge that can help me?

I had insurance through the marketplace which had me a plan through BCBS for 2019. So my baby was born in December of 2019. I called them January 1st to report her and they said that I had to do a new application adding her onto it. So I did the new application through the market place and it said I qualified for Medicaid and that I had to wait 30 days for them to contact me. So I’m still waiting to hear from them.

My question is: Would Medicaid back date to when she was born and cover her doctor visits and stuff or is my 2019 insurance supposed to cover the things she had done in 2019 and then Medicaid would back date to the 1st of January? I tried calling BCBS to ask if they cover her for 2019 and they said only the first 48 hours after born (but the guy honestly seemed very unsure) So now I’m confused on who covers all the other stuff? Because I just got a bill from her pediatrician for $1075 and I’m not sure which insurance it should be sent to. (I tried calling Medicaid and they said I have to wait for an application decision before helping me. Ugh I just want answers and to know that I won’t have to pay this huge bill.