I could guess away, but I worry that would do more harm than good.

Do yourself a favor, write down a mood log of your hubby's moods. Times, when he eats, when he takes his meds too. When he has his mood issues. If his current meds aren't working his p doc may be able to look at it. If your hubby allows that is.
Is it possible he has a diagnosis you aren't privy to just yet?

Whatever happens please as a person who's been there please don't inadvertently sabotage your husbands recovery by asking absolute strangers for his diagnosis. This is your husbands medical issue.

If I sound harsh I really don't mean to sound it, but I have had family members talk to coworkers about my mental health issues, asking them their advice, and it's backfired on both them and me.

Hopefully if the lamactil isn't quite doing the trick, the p doc might consider something else.