R.J.
After 2 weeks... I'll lay money it's not jet lag.
Teeth
Cold/Flu
Ears
Sinuses
GrowthSpurt
etc.
Try the tylenol test. As in give him some tylenol and see if he's conked out in about 20 minutes and stays asleep for 4-8 hours. If so, then you know it's some sort of physical pain that's not bad enough to be noticeable in the day, but when it's time to be quiet and sleep... it's keeping him from sleeping / waking him up.
It's REALLY common for toddlers and children to get sick over vacation because of the plane trip and new people in wherever you just were (just like starting school).
There's also a really nasty head cold going around which is about 1 week of feeling off/cranky/sore but okay and 1 week of being biserable, wiff a nobe you cant breif dru, and day head dat beels like ibts going to essplode. If you're extra unlucky you'll get the chest cold thats going around, too.