Feeding problems

Okay ladies I have a question I’ve been breastfeeding but lately my supply has been very low in the evening and baby gets really fussy when hungry because he’s not getting enough so I started him on formula but still breastfeeding I’m doing 2oz of formula and 2oz of breast milk he’s been on it a week now he was doing okay we had the ready made bottles at first but now the powder. He was doing fine with the ready made bottles same brand as the powder. I started using the powder today and he’s been throwing it up all of it and having diarrhea