Fatigue can be a sign of depression ... Especially when it's paired with lack of motivation, low energy, etc. obviously, it could be anything (even things like B12 deficiencies) - our brain chemicals are still trying to figure out what the heck this sobriety thing is, so I wouldn't be surprised if it turned out to be some form of depression.
Good luck at the doc ... And keep us posted, this is very interesting topic!