What Causes Diarrhea, Unusual Stool With Mucus And Pus?

good evening docter, i am mother of 5 month baby child, she have recurrent diarrhoea from 3rd month. during 3rd month her stool routine was pus cells around 30 to50 and reducing sustance 1plus. on this report she was admitted and received amikacin,metrogyl iv for 6 days and oral for 5days more. but after 5 days she had diarrhoea and stool report was reducing substance 3 plus, pus cells 10 to 20 with mucous present. so we changed the docter. he changed my milk to soya milk powder and add cephalosporin. she was normal for 1 week and now again she have diarrhoea with green colour stool, watery with mucous and pus. her weight is not increased form 3 rd month(4.8 kg) to till (5.59 kg) should i do her stool culture and sensitivity? please docter give me suggestion what will be her diagnosis?