Hi Lindsay - I didn't see if the doctors checked your son's iron level - It sounds like he may have an iron deficiency - slightly anemic, low recticulytes - all symptoms of iron deficient anemia - then he takes iron and things go back to normal - then they take him off iron and the problems return.... so I'd think it'd be important to know his iron levels before and after the iron supplements - Maybe he just doesn't get enough iron in his diet - some questions I'd have - How well does he eat? How much iron did they give him. What were his iron/ ferritin levels? If he's doing well taking iron supplements- why stop? Can he modify his diet to get more iron without supplements?
http://www.mayoclinic.org/diseases-c...n/con-20019327
I Agree with Greg you may need to either get a different doctor or make sure your doctor spends sufficient time to answer you questions - you may also need to be more assertive - if the doctor says its a one time thing - let him know the history - etc. My guess is making sure he gets a balanced diet rich in iron will take care of things - not always easy in a 4 year old - but doable.
Best wishes,
Paul