Help- Upset belly from supplementing ?!

Hi mamas,

How do you know if your little one has a milk intolerance? I am breastfeeding but started supplementing at night as I was afraid I wasn’t producing enough and was stressed out about it. Anyway, I started slowly and added 2oz of formula to 3 oz of breast milk but she seems uncomfortable from it. She isn’t spitting up or anything like what but her belly is bloated, she wants to have a BM so bad but can’t and is trying looking uncomfortable and lots of gas. Should I switch formula because of her reaction?

Or is this normal ?

Thanks in advance