How to know if baby has diarrhea?

My son is 3.5 months old and has gone poopy 3 times already in the last 7 hours. He isn't acting sick at all and he's his usually smiley self. The peanut buttery consistency and color is pretty normal but he normally only goes once a day for the last 2 months.

Yesterday he didn't go at all which rarely happens so maybe that's why he's gone three times?

Edit: Could this possibly be teething? He's been drooling and eating his hands non stop and last week he seemed to be quite uncomfortable with his mouth and a bit warm but no alarming fever. I just read that the frequent poops could possibly be teething but I'm not sure how the two correlate.