My Son Is In College Lives In Arizona, Had Slight

My son is in college lives in Arizona, had slight flu last week Tuesday. Felt better during the day, but at night when sun sets, feels bad again. Said his body is cold 95% of the time and can't sleep. He lives on his own not in dorms. Has been at dorms doing homework with group of people often that's when he got sick. Most of the time has apetite and big eater. Now very timid and not so much hungry. Help please. Is it just nutritional balance?