Hi..whenever there is pain in the legs I immediately start to worry. I have a 5 1/2 year old and 4 year old. They have complained of pain since about 2 1/2 like yours. I take them to the doctor, the doc checks them over, flexes their joints around and basically say nothings wrong. I think you need to get to a pedi quickly, though, just to ease your mind. Is your son limping? Is he acting like nothing is wrong if you distract him with something fun? As for drinking so much, my girls like to drink a lot, too. How is his urinating? What about potty training? What did your old pedi say? I think only regular water is something you may have to lean towards. That would quench his thirst more. The flavored waters seem to make my girls thirsty even more. I agree about the diabetes issue, too. Let us know what the dr. says. Hang in there.