I think, at 1st talk to your doctor freely. It could be actually your child is ok, you just thinking excessively .Every mother love her child, its natural .If you really doubtful, try to deal with your beloved son differently with doctors concern. You may read the following article for your help:

http://www.ndri.com/article/delayed_brain_development_for_children_with_iron_deficiency-127.html

http://www.ndri.com/article/management_of_mentally_subnormal_low_iq_children-368.html