I'm just going to say it - my DD's dirty nappies can clear out a room. She's 4 months and I think I started noticing it around 2 months? It was definitely after the HV stopped coming for her frequent visits, or else I would've asked her. I've looked online and it says that exclusively BF nappies should have little to no smell. She does vomit a lot as well despite being burped and can be gassy at times. Could she be lactose intolerant?