Birth Control making me Lethargic

Hi all has anyone tried a progesterone only birth control like Heather the mini pill? I'm 3 weeks in and I swear I can hardly get anything done, I am so extremely lethargic and tired. My LO sleeps through the night And I had more energy after he birth when she woke up 4 times a night compared to now. I've been taking naps with her but I knock it cold for like 2 hours with her and just feel so sluggish. Do you think this is birth control? Or just post partum tiredness catching up with me. I just don't feel myself.