What Causes Persistent And Recurrent Stomach Pain In Childrens?

My son has been complaining of stomach pain for the last eight nights, after dinner and especially at bedtime (we tend to eat on the late side). The pain seems to vary by day and does not seem to be increasing overall, but it is not going away. He is not doubled over but someways comes downstairs crying. He says he has not had any bathroom problems. He has not been vomiting at all. We have been avoiding milk products for the last week. My son has also been talking of stress lately although he is only 9 years old and has always been a very happy and content, easy-going and well-adjusted boy. He does seem to get concerned about certain schoolwork (but is doing well and has plenty of time to complete his work) and he also sometimes worries about the next day and has a hard time getting to sleep (he loves to read and often reads in bed for 1 or 2 hours). I don t think the stress has anything to do with the stomach pain but just mention it in case it is a factor, because my son has mentioned it to me (very bizarre for a 9 year old to be talking about stress but he has 3 older siblings). What do you think this might be? I was thinking of trying an antacid tomorrow. The other conditions I saw do not look likely as he really has no other symptoms. Are there other things we should do or avoid while figuring this out? What kind of doctor should we go to if we need to see one? He just had a well-child check up two weeks ago but didn t have the problem then and I don t want to take him back! Thanks for your help.