Some good measuring advice here... and what worked on my fourplex was a really good vapor barrier (over a bare earth floor) with no gaps, even up against wall.

In my area they usually lay the vapor barrier on the ground and insulate the walls with foam, without venting.

If they did not install a vapor barrier or have foundational leakage, you could have moisture trapped there and it could be developing into a bigger problem.  

If not, I would put down 6 mil vapor barrier, run nailers as John suggested, and install foam panels between nailers so entire floor is supported.

And they make organic vapor cartridges for respirators, you won't smell a thing!

If these are double-pane windows, the seal has failed and water vapor has gotten between the panes.

Of course, the tile and sheetrock were ripped out, vapor barrier, backer board installed, new tile properly laid and grouted. 

We've brought in two dehumidifiers which are helping, but I'm not sure what the root problem is or even who to ask for help.One contractor said moisture is coming through a hole in the exterior stucco, but another said no way because the vapor barrier would block it. 1st one recommended installing insulation, but I've also read this can increase condensation problems.

The vapors from those chemicals probably is harmful.

We moved all of it, put a vapor barrier down and vinyled the whole house.