Zen,
just some random thoughts...

Volunteer work...contact your local community services for places looking for them
My favorite one is with the Adult Literacy Project.

Tidy house? Make a commitment to do one chore a day...anything to get you moving.
Re medications and metabolism. Walking is good exercise for physical and mental health...the benefits are rewarding.

Turning down invitations...means you were invited, right? Has your brother refused to come if you do? Probably not...perhaps making some kind of truce with him is in order? By letter if in person is not possible. You can explain your side of things, let him know you are better, and offer your thanks for taking care of your affairs...

Many of the other things may fall into place once you get out and about and become involved with anything outside the walls of your home.
Another though, but I don't know if you have it there. We have a telephone check system for the elderly and disabled...they are called on a daily basis, usually at a prearranged time--subject to change for appts, etc. These folks life alone and this gives them daily contact with a friendly voice...and it makes the caller feel good, also.

Just try one so you won't feel overwhelmed...as you feel more at ease, then add more activities.
You can do this; make changes that will bring you more peace.

In Peace