You know… I was compleetly over my cold, my sinuses were compleetly clear for the 1st time in ages, and I generally felt good. I return to work, and am in the building for no more than 30 minutes and my head started filling up. I feel the crud in my sinuses again and there is a definite smell of mildew / mold in the building. Even my boss with a cronic cough said she hadn’t coughed at all almost the entire vacation, but she is back here for an hour and the cough has returned. Our newest co-worker then chimed in and commented on how since they started working here they have had a regular runny nose. I really do believe there is something wrong in this building.
I’m sure it couldn’t possibly have anything to do with the leaky roof. They replaced all the waterstained celing tiles the day before we left for break and there are already a number of them that are heavily waterstained again. The storn today isn’t helping either.
John's Musings 
There’s also a possibility that maybe you and your co-workers have developed an allergy to mold and mildew.
That’s entirely possible. I know after never having allergies ever, I was diagnosed with severe dust allergies due to the dust level in my various housings on campus at college.
Might want to check that out. I hope you feel better soon!