I hate to be the bearer of potentially bad news but I would say you have a blown head gasket or a cracked head. It's putting hot exhaust gas into the coolant. Pull all of the plugs out and pressurize each cylinder one by one with a compressor. You will need the hose to thread into the plug hole. These can be borrowed from auto zone as part of the compression tester kits. As you compress each cylinder the piston should push to bottom dead center. Listen for air hissing into another cylinder and pull the radiator cap off and look for air bubbling up through the radiator. If you find either you have a leak or a cracked head.
