I personally have never had this problem. However, a very close friend has 4 children, 3 girls and 1 boy. Her son is one year older than the youngest. He whined so much that it was starting to get embarrassing. She worked outside the home as a paralegal and knew one day that her babysitter would be late. So ... she left the children with her extremely responsible 11 yr old sister in charge for a few hours until the babysitter was due to show up. She knew this info about one week in advance and talked with all the children about it at length. However, that morning her son called 911 because his sisters would not play with him. The Sheriff's dept called her at work and there were almost serious charges against her and her husband for child neglect, however, everything was explained with interviews with the 11 yr old teachers/counselors and neighbors, etc. The mommy was so upset because her son STILL did not understand why he was punished because it was his sisters who would NOT play with HIM. Out of frustration, she took him to his pediatric dr and was told that the allergy mediation her son was taking sometimes caused this tiredness which made his whiny. We looked up the Rx on the net and this symptom was NOT listed but the dr insisted that it was not listed because it was extremely uncommon but he just knew of it due to his practice. There was an immediate positive change in her son once the new medication was administered.
That was approx. 5 years ago. Her son is an absolute joy to be around and extremely popular now. You didn't mention medication with your son but ... I write to you with this story for 2 reasons: 1) if you son even takes OTC meds - check it out and 2) Hang it there. Hopefully, in a couple of years you'll laugh at the "old" problem.