Switched from BM to formula

So I recently had surgery about 2 weeks ago and found out I was pregnant so it’s been a whirlwind of bs lol. But after surgery my milk supply dropped like completely and I wasn’t able to produce more an an oz every pumping session because I didn’t breast feed for days after recovery (I was on pain meds too). Now my son drinks powder formula and it makes me feel guilty sometimes. I went 9 months strong straight breastfeeding, barely even pumping sometimes (unless he was going to his nanas house). But for some reason it seems like he sleeps way better, has more energy, and it’s actually trying to talk more? Idk was my breast milk holding him back or something? Anyone else experience the breast milk to formula transition? My sons also been self feeding a lot too and actually loves snack time. Idk, this new mom life is like, so confusing lol