Baby is suddenly fussy with formula

I’m doing a mix of breastfeeding, pumping and formula. Lately I’ve been trying to ebf with a bit of formula when I’m too tired but baby has been fussy when drinking formula. Baby had no problems with formula before but is now fussy. Will finish sometimes but then refuses to finish nor drink at times now. I’ve switched bottles and ensured it’s at room temp but can’t figure out what else needs to be done. What do I do? #Needadvice #firsttimemom