What Causes Loss Of Weight And Appetite, Fatigue Despite TB Treatment?

We found my father got affected by TB 2yrs before. He is having a habit of drinking but now he controlled as much as he can. He took treatment for 6 months in Govt hospital then he got negative in his result. But after a month again he got postive which shows CAT II stage. After that as per docter advised him to take 8 months treatment. he is taking treatment now. They prescribed him to take streptomycin injection along with the pills. Now what my question is Though he is taking the medicine regularly (2 and a half months as of now) he looses his weight from 48 to 39 & he feels lose of appitite, fatigue, he cant even walk for a short distance. I consult the doctors also for his condtion but we didnt get any proper reply. Why he become even more worse after proper taking treatment also. Kindly suggest us what we can do further.