Putrid smell between 2 teeth, only notice when flossing.

On my bottom teeth at the back left, between the 2nd and 3rd tooth from the back there is a really hortrible smell on the tooth floss after i use it, which i would describe as rotten, what I would think 'insides' would smell like!.
It only seems to be between these 2 teeth. they both have silver fillings although I dont know that they have anything to do with the smell.
Is it coming from the teeth or gums?
No pieces of food etc come ou t when flossing, brushing or using mouthwash.
I was at my dentist just last week and got told everything was fine and just to watch out for those ottom teeth as the fillings were deep...Ive only noticed this smell since then...never paid much attention before!!
Will it ever get any better?
Found a thing called 'Oil Pulling', would this help?
Thanks :-)