Alimentum Formula Question

The Dr just had me switch my 4wk olds formula to the one for lactose intolerance issues. He's not loving it as much as the dairy formula and he's eating half the amount he was eating previously (now 2 oz vs 4 oz before). It's been 24 hours so I was wondering if anyone else experienced this if they switched. He also seems to have more gas than the dairy based formula (ugh!).