How long has the man suffered from the symptoms he described?

M: Good morning, Doctor.
F: Good morning, Mr. Smith. What can I do for you?
M: I feel there’s something wrong with me, but I’m not sure.
F: Could you explain to me more?
M: I usually get a running nose, watery eyes, scratchy throat and other symptoms on Monday. It will last for the following five days. And since I am terrible busy with my work, I won’t have time to see the doctor. But when I do have time to see the doctor on weekends, the symptoms will disappear all of a sudden!
F: And you will get same symptoms again next Monday.
M: Exactly.
F: How long have you been like this?
M: About one month.
F: Did anything special happen during the past four weeks?
M: Nothing special. Oh, wait! My company has moved from the old address to the present Mount Plaza.
M: That is it. When a new building is just finished, the chemical vapors being given off by glue, paint and other construction materials and moisture can’t escape, the building, just like people, can’t breathe properly. So it gets sick.
F: Well, I got the reason. Thank you, Doctor.
M: Wish you good luck.