I have a tiled shower in the master bathroom that started smelling like sewer gas (rotten egg/bathroom smell) but only while showering. The shower is used every day. The trap is visible and is working and there are no issues with any of the other drains in the bathroom.

I've had a couple of plumbers out to look at it but all they can really suggest is putting bleach down there. The drain has been cleaned out and there is no debris or gunk down there. The toilet does not gurgle, the wax seal is intact on the toilet, and all traps seem to be functioning in the bathroom.

I've done a lot of reading on this site and elsewhere on the internet but I'm no plumber so I would desperately like some advice on what to do next.

I think it might be one of two things. It might be the lining of shower was laid flat (house was remodeled in 2005) and so water and whatever has collected under it but I can't see how it would create that distinct sewer smell. It is not a musty odor, it smells like sewer.

The other possibility involves some work that was done on a bathroom almost directly below this one. On a Friday in June, the crew reattached the toilet and sink of a downstairs bathroom after doing a fair amount of work in the room. On Saturday, the shower stunk for the very first time. Is it possible that something the plumber did when reconnecting the toilet and/or sink could be causing this by trapping gas in the drain pipe so the gas rushes back up the shower drain when the water comes on?

This is very distressing so I would appreciate any suggestions on what to do or where to look.