Nappy rash??? Pampers nappys?

My 14 month old son only ever gets mild nappy rash when teething but for the past week he has been suffering with quite a bad bout of it. It's very red and inflamed, nothing like he's ever had before. We have recently swapped from pampers super dry to pampers active fit and wondering if this could be the cause? Has anyone else noticed anything like this? Also wondering what's best to treat this. I've been keeping his nappy off as much as possible, washing with warm water and using sudocrem. Is there anything better I can be using? Thanks x