Thanks for the replies and support!
We spend huge amounts of time outside in the morning and afternoon. We've had great weather here lately, and he's been so excited to walk that we're outdoors most of the day. One of my neighbors saw us a couple of days ago and said "he gets so much exercise, he must sleep great at night!" Huh, you'd think so, wouldn't you?!!
We aren't having problems getting him to go to sleep. We went through that phase a couple months ago, but he's been going to sleep so easily since he started taking only one nap a day. There's no way we can keep him up any later; he is exhausted when he goes to bed.
He seems tired even when he's up in the middle of the night. Fussy, agitated, rubbing his eyes - but wide awake.
Seedling, I'm sorry you're going through this too, but glad I'm not alone. I haven't made it out to the grocery store in the middle of the night yet - I wouldn't trust myself to drive - but we've also done the couch and video routine.
Like you, I'm almost convinced it's teeth, but I can't feel anything, not even a raised area, on his gums. So how long is this going to go on?
DH and I have started taking shifts, and that's helping. I take the first shift, and stay with DS until he's been awake for 1-1.5 hours. If he's awake longer than that, I bring him to DH, who's been starting the night in the guest bedroom. That way, neither one of us is awake for more than 1.5 hours or so. It isn't great, but it's working, for the moment.
Still, I hope this ends soon. I am loopy with sleep deprivation.