soy infant formula

breast fed my son til he was 4 months old and then stopped and he has to eat the infant soy formula because he was lactose intolerant. he just turned a year old and has switched to drinking whole milk. we noticed he was being fussy with drinking the whole milk and it would cause him to get belly aches so my son's doctor said to give him Silk original soy milk instead. I was researching if after I heat it the first time if it could go back in the fridge to be heated one more time after that (I haven't been re-refridgerating it but I still haven't gotten an answer yet) a little concerned when i did see this though....