Hi Natalie,
He obviously isnt suffering from the hormones (well maybe yours) and as you say he isnt unhappy about the pregnancy but have you thought that perhaps his emotions are up and down because of this daunting experience thats ahead of him?
women seem to cope relatively well when faced with this life changing time but men are the providers (by nature) for the family and its quite a shock to suddenly realise that the family will expand and they are responsible for a new life.
They dont have the hormones and the instinct to naturally bond with a child that isnt born yet and its probably a bit scary for him, even though hes overjoyed.
Sit down and have a chat with him, talk things through and you'll probably find out that hes just a bit concerned, for you, for the baby and for the future.
As for the tiredness, i remember how i used to get home from work at 5, eat my tea and be asleep by 7. Id wake up enough to have a bath at 10 and then climb straight into bed and sleep til 8. My social life got put on hold until i got my energy back which was at about 10-12 weeks.