Sorry to hear about this cyst that you are dealing with. Sounds very painful.
I haven't used Black Salve on a cyst but have had excellent results with tumors on my nose and several on my dogs. One of the tumors on my dog was very large and hideous looking.
The salve killed all of the cancer and the tumors fell off.
It might be worth a try. You will know if the salve activates or note if it builds an eschar.