Is This Good Or Bad?

Just recently started giving my baby the Similac Soy Isomil milk formula.. A soy based milk coz shes too gassy on other milk (already tried nan optipro, nan sensitive and similac tummycare).. For those 3 milk, shes usually very gassy and very cranky.. She also poop per 3 to 5 days. So we asked her pedia if we could try this milk. The first night she drank this milk, she immediately pooped. Well its runny. Almost after every feeding with the milk, shes now pooping but with a runny poop. At times mushy but most of the times her poop are runny. Should I change milk again? Or wait it out?