What Causes Persistent Greenish Loose Stools?

My son is 5 months old. Is getting green poop watery on the 5 the day of using walamysin suspension.he was detected with mild infection after which was suggested above antibiotic with nutrolin b syrup. He is exclusively breastfed. He is passing watery poop from last 2 weeks. He was given rotavirus dose almost 7-8 days back.before giving this dose he was facing the loose motion problem for which was getting the neopeptine dose.