If your stools are truly black, that is a sign of bleeding. If they are green, it is probably from bile. There are meds they can give you to help with the diareah to harden it up. Call your dr and get in there. You need to find out if you are anemic from blood loss with the black stool.
I get a lot of upset stomach and burning now since my gallbladder removal. It seems like my stomach is always burning and hurts all the way up to my sternum area.
My gallbladder/liver area still hurts quite a bit, and I ended up with a bad case of costochondritis from surgery that i am still dealing with.