A creative hobby is great because you can pick it up and put it down as you want and it allows you to express how you are feeling. Whether thats through painting, sculpture or song writing. I would avoid trying to play an instrument unless you have already mastered one since that can be very frustrating. Volunteer work is a great idea for getting you out of the house as well. Perhaps you could combine the volunteer work with the creative hobby?
Hiopefully things will improve under the new therapist and this is just a temporary glitch.
I didnt realise you had been diagnosed with BP and were on meds either. Is it possible that one of the drugs is not being very effective and needs changing? The Bipolar forum can also be a mine of useful information. I would still look for a hobby though. Creativity allows expression and some people find that really help them... Just my thoughts