Hey Tom, first few months I was wrecked by 4/5pm, used to come home from work and just crash!!
The body needs time to repair and heal, 17 years of drinking is going to take more than a few weeks to bounce back from, it's going to take time.
Don't fight it though, give your body what it needs, if it's an early night go with it and eventually you'll get your energy back!!
Hang in there!!