Fumes in Bathroom - help!

We are renting a 2 bed 2 bath and have experienced acidic paint fumes in our bathroom. The smell worsens at night and in the morning. It seems to be coming mostly from the shower. The toilet is right next to the glass shower but the smell seems to be worse in the shower area. The smell intensifies and wafts into our bedroom and we have to open a window.

We have had a plumber, HVAC, and drain guy visit. The drain guy didn’t clean anything bc we already did it. The HVAC guy said he couldn’t do anything. Plumber is unsure.

We have also done the following:
•not the p-trap as we have filled them with water
•cleaned out all drains from any gunk
•valves under sink were changed/tightened
•when air conditioning is running it intensifies the smell. We are wondering if it just circulates the air.
•natural gas company came and checked - all clear
•running the fan doesn’t work - occasionally makes it worse

We smelled it outside of the building near the sewer gate in the alleyway. The surrounding apartments didn’t have any tenants for a month or more. One did clean their carpets when the smell began. We live on the end unit of the building.

Any thoughts would be greatly appreciated to help us resolve this!