u/ConfidentSet6510

So, I have this problem that happens sometimes after showering.

It smells like sewage, like bad. I’ve noticed it mainly when the AC is on. If the AC is off, I don’t usually smell it. The smell if usually isolated to the bathroom but occasionally comes through the nearest bedroom air vent as well when it happens. Any ideas what this could be? The home is on a septic system as well if that matters.