Hi Doctor. My Baby Is 9 Months Old Now. All

Hi Doctor. My baby is 9 months old now. All sudden for last couple of days I have seen some rashes like Hives. Not sure why. Especially post giving formula milk immediately after 10 mins it's start. Is it something allergic to milk or it's just common inkids. He is taking this formula milk from his 2 months along with Breast milk.

Can you pls suggest.