Thanks everyone, your a great help.

It's hard not knowing what to do. My DD suffered really bad reflux and I didn't give her anything until she was 6 months old. However, DS is constantly hungry.
I have changed his formula from S26 to Heinz and he seems to be coping better. If I try to give him more formula, he tends to push the bottle out of his mouth and then screams a minute later for food.

Thanks again ladies, your a great help.