this happened to my son also, surprisingly he was on Gentlease too... But in my case, it smelled different.. it reminded me of throw up.. i didnt worrry the 1st night, bc all babies spit up / throw up... but second night worried me, so we went to see a doctor.. He said he was a little constipated, the formula thats been sitting in his tummy came back up with foul smell, b/c it's already been digested. It was cottagecheese-looking stuff, not very pleasant... So if thats the case, add ask your doc for a laxative and maybe switch formula. But honestly, babies that young cant tolerate ANY formula.. my son went through 4 different ones in 3 months, only to come right back to the first one, Similac Advance, the doc. told us he'd have softer poops, and he does. Good Luck to ya, hope you figure out the problem!