Some people have developed a life-threatening condition called
lactic acidosis while taking
metformin. Get emergency medical help if you have any of these symptoms of lactic acidosis: weakness, increasing sleepiness, slow heart rate, cold feeling, muscle pain, shortness of breath, stomach pain, feeling light-headed, and fainting.
I am not saying this is whats wrong however I think you should be aware of these things listed.
I would call the doctor if he gets worse.......I would call anyway!