What Causes Persistent Severe Cough And Fever In 65 Year Old?

Hi, Father (65 age) is having severe cough and temparature from last 3 weeks, his voice is nearly gone, he is sleeping nearly all the time, lost his weight and looks very week. Went to doctor 1 gave some medicine suspecting flu but no effect changed another doctor 2 gave some new medicines suspecting typhoid and again no effect, now have to change the doctor. please advice what do you recommend. Many thanks, Lotus