That's what I thot @bbhope. He has no extra gas and no other symptoms. I guess 2 x diarrhoea (only tiny amount tho with a little brown mucus) would be considered mild diarrhoea? But he does go 2 more times but seems to not be diarrhoea. But it is green and his normal poo's are mustard colour.
He is only getting about 180ml formula a day atm but if it's allergy it wouldn't matter how much he has right? Any amount would give a worser reaction than just diarrhoea.
I would try lactose free again for now until he is def back to normal and then slowly mix in nan comfort again or whatever normal formula he handled best.