Hi, I have a low body temp. In the 80's a doc did a lot of research into low body temps and how it effected the body. People who had a low body temp on a regular basis were diagnosed with Wilson Syndrome.
Many doc's didn't accept it as a true medical illness though so it became quit ignored. The theme of the diagnosis was that even though the Thyroid was putting out all the stuff it was supposed to be doing the body was too cool for the catalyst to do it;s job. The enzyme was there but could not go through the chemical reaction needed for it to be used.
My DO thought this was what I had. He gave me some meds and I lost 30 lb.s in one month. I felt so much better and healthier.
I would call the pediatrician in this case though. It is not a normal expected temp for your son, if he was normally low you would have noticed when they took his temp before especially when they started taking it over and over.