Loose Poops And Vomiting

Our son is 2 months old and is having loose poops since last week or so. First he was on mother feed + meiji(once or twice a day) but then 2 weeks ago my wife had an operation on one of her breasts because it was infected quite badly and the concerned doctor said not to give mother feed to son. After that, our son was only on bottle feed (meiji) and started having loose poops and then we visited a child specialist and he changed meiji to similac. After changing bottle feed milk (meiji to similac), loose poops stopped for a few days but then again he started to vomit and loose poops started again and now hes pooping 10 to 12 times a day. Can you kindly suggest? Im very worried for our son.