Unable to gain weight. Gaining weight.

My sister, 25 was started on Akt 4 initially on September 15th. Then in october first week she developed drug induced jaundice with abnormal lft. Then doctor stopped ATT and treated with Ethambutol, Amikacin and Moxifloxacin for a week. Then he added Rifampin alone with Ethambutol and Moxifloxacin. As it was tolerated he added Isoniazid too and it too tolerated. Now she's on Rifampin 450, Isoniazid 300 (RCinex) and Ethambutol 600 (Mycobutol) with Pyridoxine 40 (Benadon). She also underwent exploratory laparotomy before starting ATT as doctor was not able to identify the cause of extreme loss of appetite, weight loss, abdominal swelling and ct suggested of small bowel perforation. Then everything was cured and her appetite improved. Before jaundice, she was 40 kg. After jaundice her weight reduced to 38.3 kg. Now lft is normal. But she has gained only half kg in the last month. But doctor saying not to care about weight as she's feeling better. Please tell why she's not gaining weight.