My son use to eat 3/4 oz every 3/4 hours and lately he eats 1oz or 2oz and even if he goes a long…

My son use to eat 3/4 oz every 3/4 hours and lately he eats 1oz or 2oz and even if he goes a long time without eating he will still eat that. I'm really concerned and the thing is he's not sick. No fever or green mucous. Just some diarrhea. Could it some stomach flu or something ? He's 2 months old