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

M：Good morning, Doctor.
W：Good morning, Mr. Smith. What can I do for you?
M：I feel there’s something wrong with me, but I’m not sure.
W：Could you explain more to me?
M：I got a runny nose, watery eyes, sore throat and other symptoms on Monday and they last the following five days. Since I’m terribly 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 suddenly!
W：And you will get the same symptoms again the next Monday?
M：Exactly.
W：How long have you been like this?
M：About one month.
W：Did anything special happen during the past four weeks?
M：Nothing special. Oh, wait! My company has moved into a new building.
W：That’s it. When a new building is just finished, the chemical vapors of paint can’t escape the building, so people can’t breathe properly. So they get sick.
M：Well, I got the reason. Thank you, Doctor.