One thing you might consider, that helped me: modify your agent's personality to suit you. You may be exhausted because you're talking to someone you don't like all day. I've instructed Claude to talk to me like Confucius, because I have philosophical taste, and it makes a world of difference in terms of how I feel at the end of the day.

Claude's default personality is a bit too combative for me. Another instruction I've given it is "don't argue to win".