How old is your son as well? Ive always been told that you shouldnt be doing any heavy weights whilst you are still growing as you will divert your energy into growing healthy strong bones into muscle (so he could be shorter than he should be and may have complictaions later in life).
Theres a few threads about whey powder, I get a worse stomach from exercising anyway, so not sure if whey protein is making it any worse or not, but defo found the more expensive ones (PhD, Omni, Maximuscle) to give much better results than cheap shop bought ones (even from health shops)