For a while now I've been getting constipation, and a few times I've had this bad odour/bad taste in my mouth, something like fesces. A few times I've spat out some yellowish thing. Once it was stuck in my throat and so I spat it out on to a tissue, and it smelled like fesces.
I first noticed the taste while I was playing sports (Badminton)
Hopefully this is helpful enough.