Hi, what could be the source and cause of halitosis – bad breath? The only thing I can associate this smell with is a stable/horse

. I’ve come across this smell quite a few times in life – among friends, even in my family – so I don’t think it’s some super rare or hidden issue. But they had it temporary.
As for myself, I have a problem with post-nasal drip, a sour taste in my mouth/on my tongue, a coating on the tongue, and sometimes heartburn. I used to have tonsil stones, but for over a year now, nothing has come out when cleaning.
Do you have any suggestions?