Talk to Pediatrician on Baby Has Diarrhea

My 8.5 months old baby has upset stomach for the last 5 days - he is passing 2-3 stools in a day which are yellow and liquidy (3 times in 5 days, his poop was watery)... I am giving him Bananas and unsweetened yogurt + Breast milk + 1 formula feeder at night time... Since we traveled last week so initially I thought it might be because of changed env and water (which I boil always) but it has been 5 days and the problem doesn't seem to settle... Baby is active and not cranky.... Should I give Flagyl to him as was recommended by a doctor who I personally know? If yes, how many ml? And What food should I give him?