Sheetrock on Walls Is Falling Apart and Cannot Find the Cause

In the corner of my bedroom i have discovered that the sheetrock on each wall was so damp that it is falling apart. One wall backs up to my shower the other wall backs up to the laundry room further down on the other side of the wall. The walls are connected and both are damp enough so as not to withstand pressure. The wall that backs up to the shower also contains a return air vent.

I was thinking it might be condensation so I put a bucket of Damp Rid in it to see. When I went to check it this morning I saw a water mark on the concrete floor and the adjacent piece of wood. At this point I took a 30 minute shower to determine if that what was causing the damp marks. The marks had not expanded (I had outlined them with a marker) so it must not be the shower. I am now washing clothes to see if that may be the problem because I don’t know where the water lines run. Also the walls on the same side as the washer are not damp at the base or walls.

I’ve had several professional Plumbers, HVAC Contractors in to look at it and they can’t tell me what is causing it dampness in my sheetrock.

Several years ago when this same problem occurred, the man who came to clean the duct work in the house sealed the return air duct and said there was condensation there. That was around 5 years ago an apparently it happened again, only this time my carpet is not wet and there was no odor so I didn’t realize I had a problem until I removed the air vent and felt the sheetrock.

I know this is a long problem but I just do not know where to go tor who to call for help.