Formula (and all cow's milk products) can cause tiny tears in the lining of the intestine, that are essentially impossible to detect, but can lead to a predisposition to allergies and stomach troubles. If you think your lo has tummy troubles, I would look to the formula first, the solids second (and I just can't imagine feeding my tiny tiny baby solids), and then to changes in MY diet. I would (and have done it with both of mine) eliminate dairy, egg and wheat--all of which can cause breastfed babies to be gassy.
both of mine were infrequent poopers. Waylon went today--with a grunt and sigh he had everything covered in it. There was more than I could even believe.