Cat Keeps Scratching Scab Outside of Ear?

My cat is a 4 year old Domestic Shorthair. He doesn't go outside except once in a while to say hi to me while I'm sitting outside. He has had a scratch right outside of his ear for awhile now and constantly scratches it. He will dig in his ear and when he shakes his head, clear liquid comes out. His ear looks pretty clean, barely any black or dirt. He won't stop scratching the scab, which has made his skin raw and bleeding. He does not show any other symptoms, etc. I do not know what to use without taking him to the vet, which I would like to avoid. I have tried ear mite liquid, along with ear wax buildup liquid, nothing seemed to help.