What Causes Vomiting Along With Red Rash On Face On Feeding Isomil To Infant?

Hi Dr. I breastfed my 10 wks baby for 8 weeks but had to stop because she is lactose intolerant and started giving her InfaSoy, it used to constipate her so started her on Isomil 1 yesterday, she threw up this evening and has developed a red rash on her face. Could she be allergic to Soya as well? Please help Pabi