Your ped. is right - if your kid is hungry, he'll take the bottle. Kids go through "feast or famine" phases, where they'll eat ravenously for a while and then their appetite will diminish. Our 5-month-old is currently in a "famine" phase where he's eating perhaps half what he used to, but he's still hydrated and happy and energetic, so I guess he's just developing in other areas and doesn't need as much food right now. We tried all different bottles with this one as well, figuring maybe they would ease his colic, but it didn't make a difference and we're back to the first bottles we used, same as with our first child, and the baby will take it, but only if he's hungry.