He could still be ill without showing any symptoms yet. I wouldn't be forcing him to have any milk if he doesn't want it, but to let him guide you if he is hungry (I know I would hate someone trying to feed me if I didn't want it). If he doesn't have a temp, then he possibly wont get dehydrated that quickly if he doesn't drink for a few hours. If you are definate that there is a problem then take him to a Gp or the hospital and trust your instinct.