as silly as this sounds.but i'm sure other mums will agree,does she bring baby's wind up regularly when feeding? try giving just a little milk then "burping" baby then more milk..i might add some babies like being put over the shoulder for this,some like being laid on their tummy on ums knee,and some are better if you sit them on your knee with one hand under the babies chin and rubbing its back.
god now i'm feeling all motherly
