Infant loose motions. Baby will be ok?

Hi, My four month old boy was having enfamil formula when an elder in the house introduced diluted cow milk in his diet. He was OK for 15 days & suddenly his motion turned grayish black. Stool test confirmed occult blood positive. Pediatrician asked to change formula from milk to soy. It worked. However after?3 weeks due to shortage of Isomil we gave enfamil for one day & the grey green black poop returned. We luckily got Isomil the other day and put him back on it. But he's been passing semi solid and little water like motions since three days. Doc has now prescribed entrogermina for 5 days and z&d zinc 0.3 ml morn and eve for 15 days. Baby has has two doses of entrogermina but it hasn't helped. He's still paying loose motions. Please advise how soon will the drug show its effect and if my baby will be OK? Thanks.