My sink is backing up I can turn on the disposal and the water goes down but when I turn the disposal off the sink backs up again, also my dish washer is connected into this drain, there is no water backing up in the dish washer---help

My sink is backing up I can turn on the disposal and the water goes down but when I turn the disposal off the sink backs up again, also my dish washer is connected into this drain, there is no water backing up in the dish washer---help

You have a blockage in the lateral,(horizontal ) line in the wall. The reason you haven't got a back up in the dishwasher is due to the high loop in the dishwasher hose.
The solution is to remove the "J" bend from the trap and send a snake up the trap tail into the wall. You will hit a elbo about 6 inches in but once past that you only have 6 more feet of cable to put out. Afterward flush out the line with hot water. Good luck, Tom