Just wanted to say that you are not alone - I have one of those!
My son also started in September and has had a very rocky ride. Going from a tiny village primary to a 1000 plus, extremely competetive grammar has come as a massive shock. It's not just the work (you're expected to be outstanding in everything), it's the longer day, the travel, the making new friends - all in all it's an awful lot to cope with.
The tiredness seems to affect all these kids - 2 hours homework a night doesn't leave much time for relaxation, does it?
Is your son making new friends? For the first term, my ds found it tough as everyone else in his class went to 2 other primaries and he knew no one. After having several boys home for tea, he does now seem to be making quite good friendships, but it does take a while.
So far as your son's confidence in class is concerned, is he worried that he'll be laughed at if he gets the question wrong?
It sounds like you're doing all the right things as far as early nights etc are concerned, but is he getting good quality sleep, or are things going over in his mind, keeping him awake? My ds is a good sleeper, but I thought maybe if yours isn't, he should do more exercise?
The other thing is maybe to see if you can help him organise his time better re. homework, sitting with him to keep him on task - my ds will take longer than necessary if I'm not there, he just seems to go off in a daydream.
I must admit also spoiling him in terms of packing his bag for him, writing things on his hand that he needs to remember (hope I won't still be doing this stuff when he's 35!)
I know the schools think we should just throw them in the deep end, but I feel that at least for this first year, the more support we give them the better - they seem to have a million and one things to remember every day.
Hope this helps.