Hello and Welcome to healthcare magic forum! All formula milk takes time to adjust in the body, vomiting is not from the dexolac it is from the cold that your baby has, usually babies tend to throw up when they have upper respiratory tract infections and congestion in the chest, so i would suggest you to just give your baby little quantities of breast milk in short intervals during this phase of cold as breast milk more easily digest able than formula milk however as u said that you re not having sufficient breast milk i suggest you to give dexolac a little more diluted so that it s easy for our little one to digest it. You can continue using dexolac along with breastfeeding! Wishing your baby good health and to you happy parenting!