I just stumbled upon this thread and the OP's description of her son sounds a lot like my own---I'm wondering if there can be allergies/intolerance without any poop issues (I don't know how to phrase that more pleasantly--sorry!) My son has a lot of the same behaviors the OP mentioned---he spends a lot of the day whining and crying and throwing tantrums. I've always just attributed it to his spirited personality, but now I'm wondering if I'm missing something. His appetite is pretty typical of a two year old, he snacks throughout the day but tends to be pretty picky and doesn't eat much at mealtimes. But he doesn't seem to have any issues with digestion---no diarrhea or pain that I know of (not sure he'd be able to verbalize pain if there was though.)
I think I'll eliminate dairy for a bit to see if that helps, but I thought I'd see what you ladies know about this and whether dairy allergies always lead to digestive problems.
http://www.mothering.com/community/t/1358506/food-intolerances-and-behavior-issues-help/20#post_17066480. Here is a thread I started that may be helpful to you. Dairy made a hue impact on my son. Two years later something else in his diet is bothering him which I'm trying to figure out.