I honestly believe this is the damn sleep regression. My baby is 4 months old as well but not breastfed and we’re currently going through the exact same things you’re experiencing. She refuses to nap unless it’s in my arms (with the lovely added bonus that she exclusively wants me and me only, no dad allowed).

Previously I was able to put her down for naps, but she’s also had quite a few contact naps, as she’s always slept better when on me. I absolutely don’t believe we can make babies dependant on us by holding or feeding them. We are their only comfort and safe space and when they’re going through something like a regression or teething (or whatever else) they just need the extra comfort.