3 month baby pooping too much

Maria

My 3 month baby has been pooping after each feeding not runny but she poops at least 3xs after each feeding. Her pediatrician told me to give her soy formula and I did but she won’t take the milk the little bit she did it made her really gassy and I noticed it was harder for her to poop and just this morning I notice she pooped really runny. Has anyone had this problem?