We have a four month old Shih Tzu and have had him now for 4 weeks. We are crate training and the first two weeks were great. He slept all night in the crate and would be in the crate during the day while we were at work ( no longer than 4 hours at a time). For the past week and half he has started waking up between 2-3 am, doesn't matter if we put him in at 9 or 11pm. We take him outside to do his business (he knows why he's out there, hardly any accidents in the house in the past 2 weeks) and he wants to run back inside, have to be stern with him to go potty. He will go, its very quick, and then we take him back in and put him back in the crate (not treats or play, I really don't even say anything). He will then start barking , whining, etc. at @ 4am and will go until we get up around 5am. Two nights ago he started at 3am and I put him in the garage while in his crate (he had the 1 and 4 year old up as well, not a pretty sight).
Any clue to what happened? He doesn't fight going into his crate, in fact, he will go in on his own while we are all there or have a friend over. Even this morning he didn't have to go potty, he wanted to be up and to eat.
One last thing, in the evening we play with him until he is done. Fetch, running, you name it, he's getting his exercise.