are there other symptoms?
my first reaction is to think it's reflux, as this is my business;
my mamasource listing:
http://www.mamasource.com/business/14059862321568677889
does your baby have painful, foul-smelling gas? does he strain & grunt to poop and then, when he finally DOES poop, it's soft & not hard??
does his poop have mucous in it? can look like snot, like the stringy part of the inside of a banana peel, like jelly, like the curds of cottage cheese...it is NORMAL to have poop like this once in a while, just not ALL the time.
If there is the gas, straining to poop and the mucous, then it most likely is digestive issues like reflux combined w/ sensitivities to milk protein (NOT LACTOSE!!! but milk PROTEIN) and soy protein, either in his formula or via your diet and your breastmilk...
if poop is fine and gas is fine and pooping is fine, it still could be reflux...or teething...my first had reflux (SEVERE GERD) AND got his first tooth early...
hang in there!