Hello I don't have any answer for you but I can sympathize with your pain. I'm currently suffering from a bad tooth. I'm trying to get mine taken out. I'm seeing the third dentist this week. Reading your post has made me more determined than ever. Good luck. I hope you will post to let us know what you decide to do. And when your'e feeling better, let us know what worked.
sometimes after a root canal the tooth needs time to calm down. if pain increases or doesnt start to get better go back and have it checked. it might need a bit adjustment or in worse case scenario a root fracture could be involved.
cavities cant start on the inside of an intact tooth maybe the dentist meant under the gum line or between the teeth. four years is a long time to go without dental care. regular care helps prevent many problems. rembrandt products do not work any better than most other common drugstore products and can not replace dental cleanings. good luck!