Have you been eating lots of veg, like radishes or something? If not its most likely just a stomach bug that's lingering. I had it before and it was so stinky it was like little passing wind from my behind from my mouth and was terrible. Lingered in the room and gassed my bf out. You can take alka seltza which is supposed to neutralise stomach acid. It tastes disgusting though. I eventually ended up with bad guts and it went. BUT more recently ive had sewer smelling burps and discovered it was my recent craving for radishes! I had to stop eating them as I was constantly burping and stinking the place out, it took me a few days to realise it was me! lol x