Wow. I think for anyone dealing with what your husband is, ( the combination of this time of year and the fact that he hates his job and has lost both his grandparents earlier this year) would take a toll on anyone regardless if they are bipolar or not and through them into depression.
Knowing that, plus the fact that he is bipolar I would definitely make sure his therapist and pdoc are aware of all that he is going through. It will help them both to understand where all of this is coming from for him. It may have nothing to do with how his body is metabolizing the medications but everything to do with what he is going through in life right now. He may need more therapy appointments closer together to help him get through this difficult time of his life right now.
I'm sincerely sorry for your husband's loss.