There's a smell killing me and I've tried everything ... help!

[Salman V.]

I have a 6 unit apartment building. There was a moldy mildewy smell coming into both of the two bottom units that are below grade. 

I fogged it for mold .

I used a concrete sealer on the floor. 

I inspected the main sewer lines from the toilet all the way to the street.

I painted the apartment.

I tore up some walls.

I found some wet spots on the floor. It looked like it was coming from under the floor so I thought the concrete sealer would fix it. Unfortunately, the smell came back. I can't pin point where it's coming from but it smells like must/ mold/ mildew. It's getting more and more intense. I am worried since I recently renovated it, put in new carpets and everything.