Baby poop question

Abby
My son is formula and breastfed. Some days it's more breast, some days it's more formula. He usually only poops one time a day, every day. Today he has already pooped 3 times and it seems not as thick as usual. It isn't runny. Does he have diarrhea or is it just bc I breastfeed too? (He has only been getting formula for about a month) he is 3 months old.