Ok my 18 wk old ds2's poo and wind really smell bad. All he has is formula. ds1 now 2.5, had yellow runny poos that smelled of miklk, but ds2'2 are really foul smelling and very dark green. Is this normal? He had yellowy ones at first while on coleif come to think of it but as we weaned him off it they've got less regular and pretty foul. Any advice gratefully received x