End of my rope. Awful smell from root canal tooth.

[cryingaboutteeth]

Hi. I'm a 27 year old woman. I had a root canal done about five years ago on my #31, and I messed up by not going back for the crown. They said they put in a permanent filling, though. Debris of food kept getting stuck between that and my #30 though, and one time a few months later I felt something snap while absently using a fork to pick at it. I checked it up with the dentist they told me it was fine, but I think some of the filling broke out though, not sure, and then I'm not sure when but I started noticing a horrible, fecal odor from the area. If I touch it with my tongue I can smell it on the tip of my tongue. I rub cotton between my teeth in that area and it smells awful. This has been going on for about four years. One time I massaged my gums and felt an awful salty taste in my mouth, dunno where that came from. Haven't been able to replicate it. I keep going to the dentists but they tell me nothing is wrong. At one point they noticed an abscess on the x-ray below the root canaled tooth, but it seems to be gone now. At one time I was put on antibiotics for a wisdom tooth extraction (which I didn't get done, but that's for another day) and the smell seemed to be temporarily gone. Recently I went to a dentist and they decided to place a crown on said tooth, and shaped it for the fitting. They told me the odor must be from the food getting stuck between that tooth and my #30, though I know the smell starts almost immediately when food (or even coffee) touches the area and I brush and floss as much as I can every day, to no avail. I asked them if my #30 was decaying/infected but they said no, though another dentist told me once that it was? They tell me they see no visible issues. The gap between both teeth is wider now from the reshaping, but the smell is still an issue, even if perhaps a little less than before. I keep sucking at it and feeling horribly gross. There's always a bitter taste in my mouth, my breath never feels fresh. I'm losing my mind and I don't know what to do. They tell me the x-ray looks fine, and there's no abscess now. Please please I'll take whatever advice you have. I gargle with chlorhexidine mouthwash now and then, but it doesn't help for long. Even if food gets stuck there for a short term, like maybe ten minutes, it smells awful when I floss it out.

Should I let them place the crown? Would it help?