I had to get a root canal on 2 teeth that already had crowns, so a slightly different situation, but still took several months. First it took months and months to get a diagnosis that it was infected since the infection didn’t show up on normal x-rays and dentist said tooth was fine (even though I had intense pain) I finally went to a specialist (periodontist I think) who immediately figured it out and used a special kind of x-ray to find the infection. And also that another nearby tooth also needed a root canal.

Then it took a month to get an appointment with the endodontist. She was great, but the one tooth was broken and couldn’t be saved. She went ahead and killed the root though, so it wouldn’t be so painful. There was also a lot of bone loss because the infection had gone on for so long. So another month to get back in with the first specialist to pull the bad tooth and do a bone graft (putting bone granules in the hole–very expensive but needed). Then weeks/months for things to heal including areas damaged by the infection. The whole saga went on for a year.

Just like with medical stuff, everyone is a specialist now and you have to go to different ones for each aspect of the problem. And each specialist takes a long time to get in to see. I wonder since yours is the very back tooth and it was in such bad shape if it would be easier/better to just pull it.