I know how you feel.
My teeth are crooked due to an accident from childhood, and yellow due to the fact I didn't brush them enough as a kid.
Now I'm living with the consequences.
I brush 2-3 times a day and use mouthwash straight after each and every time.
I've been doing this for about the last 2 years or so when I started brushing them seriously again.
Niether my teeth or gums have improved at all.
It feels like all I'm doing is stopping them from getting worse, but they're not getting better.
Plenty of cavities, all adult teeth at this point, unhealthy looking gums, officially have one spot where the adult tooth is mostly gone except for the very bottom of it.
I was supposed to get a plate/braces but the dentist always told me to go back home and brush some more before they'd do it.
Well, I do that every time and they always send me away again.
I don't really care at this point, though. I just wish other people didn't care so much about good-looking teeth.
There's some spots in my mouth where I can't brush a tooth because another tooth blocks it, so cavities have built up in the spots I can't touch, and I'll probably lose that tooth one day.
Fillings are absolutely useless. I hate them, I hate the feeling of them in my mouth and they usually decay after a day or so anyway.
My diet is perfectly healthy and rich in calcium. If it's had any positive effects I certainly haven't noticed it.