My Neo Natal nurse told me to give the boys a teaspoon of freshly squeezed orange juice or Prune juice in half an ounce of cooled boiled water once a day until there is a bowel movement. The formula mine were on (prem formula) had more Iron in it and caused constipation, so I was told to do the orange juice thing regularly to keep bowels moving.
My boys are now on SMA and don't have a problem with constipation anymore but I've read many people talk of constipation with SMA, and I suspect it's because it has slightly more Iron than C&G, so probably stick to C&G if things settle down.