Introduce baby formula milk

My baby is going to be 5 months and she’s fully breastfed till now. Recently I’ve been noticing my milk not enough for baby. So I tried giving Enfalac A+ and she vomited like A LOT. I got so scared and then doctor suggested me to try Enfalac GE (gentle ease) but still she couldn’t take it and vomited a lot again. I’m scared to introduce any other brands but on the other hand my milk is low. Trust me it’s so scary to see my baby’s reaction towards formula milk. I’m lost on what to do.