donot worrry, the loose stools can be secondary to advent syrup. it is one of the known sideeffect. u can stop that syrup if u think the loose stools are very severe else please continue it but make sure u give enough fluids in order to rehydrate him. if in case u need to stop it and his infection is quite severe, ull need to start him on another antibiotic, may be tab. azithromycin
100 mg 1 and half once a day for 3 days.