There is five six cause of mouth bad smell or bad breath. And we called it as Oral Halitosis, one of the reason is gum disease, food lodgement,
liver issue,
kidney issue, or any habit and psychological too.
I will suggest you to brush with soft bristle brush, do flossing, and after 10minutes use Perioguard mouthwash or chlorhexidine mouthrinse, rinse your mouth for 1min spit it it out . Don't eat and drink for 30 minutes to make sure mouthwash gets into all the spaces of ur mouth and teeth.
It will give definitely result, guaranteed