Yours description suggest you might have periodontitis or pyorhea. You should visit dentist and get scaling polidhing done. Bad smell  bleeding during brushing are other signs of periodontitis. You may not feel pain but slowly your teeth loose gum attachment snd bone loss snd teeth become loose. So better start treatment early

Go for opg xray

Foul smelling secretion from the gums can definitely be a sign of him problem. In case if him disease there will be pockets where there is chance of food logement and is not self cleansable. This food get putrified and can give rise to foul smell.

This is due to poor oral hygiene. You need to visit dentist and get scaling and polishing done