Definitely consider yeast, and constipation...

my son does this all the time. He actually was up last night from 1 am to 5:45 in the morning just talking, whispering and laughing. I find that if I start his bedtime earlier, he gets better sleep, but also, tuning out tv and electronics helps calm the brain and prepare for sleep. He is very active, so when he has active days or is overtired, he usually scripts in the night. We also tried melatonin. Used for about 4-5 days and then stopped, just to get him back on sleep cycle. He does not do it all the time, but the days he does, he is up for hours!

I would suggest finding a pederiatric neurologist who also works on sleep. They may suggest melatonin, a sleep test, other medications etc.

Neurotherapy really made an astounding difference for my son. It helps balance the brain so it actually treats the problem, not the symptom. Basically his brain was over-firing and it calmed it down.

Melatonin first, ask your PCP. They recently prescribed Seriquil for my daughter. Within 30-45 minutes, she's down for the night 90% of the time. Again, ask your ped about these options.