Hi, how are you doing? My brother has had cold or flu symptoms every few months. He has had symptoms such as chills, night sweats the next night lasting four to eights hours. When he lays down he gets a headache, feels week all while it lasts which is 3 to 7 days. Has no appetite at all. While experiencing it in the winter he thought it was just a cold. But now it is back again and there is no flu virus going around. Wondering what it could be? Can you help please, thanks.