Is Zifi Good For Baby Having Pus In Stool?

Hi, My son was born 1 month premature.His birth weight was 2.385 kg. Right now he is 50 days old and his weight is 3.21 kg. He has a problem that he passes very small quantity of stool every one to two hours or so. Stool is yellow mustard in colour. Other than this he passes good quantity of stool atleast 2 or 3 times with a loud fart.His anus area has become red now. His paedatrician first suggested stool test. Stool test showed pus value as 2-3 hpf which doctor said is ok. Hence he suggested giving him Vibact for one week. But still the problem persists. Today again when we called him, he chamged the medicine to zifo 50 oral suspension. kindly provide your inputs on the same.