My 8 year old son has eaten very little food for 3 days and today is starting day 4.He has no appetite and off and on dull bellyache , and pale in color. When I do get him to eat he only eats a little bit and stops because it causes a dull belly ache, if he doesn t already have one. 95% of his time for the last 3 days has been layin around watching tv. No vomiting, diarrhea, or fever, and he is not constipated. Took him to the doc on day 2 and was told to just keep an eye on him. How long do I let this go on, before taking him in for blood work and such?