@keka, that's the same thing we went through my baby's Tummy was so upset and she would scream all night. I'd recommended trying a sensitive formula or a lactose free one before you going straight to soy. He could be lactose intolerant
My baby had a lot of problems when I switched her to formula from BF and I thought she needed soy but even that upset her tummy. We us supplementation by similac which is supposed to be close to breast milk nd it seems to be helping