Change in poop for 6 month old

Hi so I'm going to give a background I stopped breastfeeding for almost 10 days and my son is now strictly on formula and he gets baby food once or twice a day. When I breastfed it was 50/50.. on last weekend he had a cold for about two to three days recently during those days when he was sick I noticed that when he would have gas it would have a different smell. I also started to notice that he's pooping more often and that the consistency is different it went from a hard stool (dark color) to now a light yellow mustard slimy kind of stool. I called his pediatrician and she told me that it's normal because he's changing from breastmilk to formula and that everything should go back normal within 2 weeks but my son has been having difficulty sleeping throughout the night and I can now see that it's from tummy problems and also I just fed him a bottle and he's pooping already so I'm starting to think it's diarrhea or the formula is too harsh on his tummy. Please help.