Could also be fungal, or a mixture of both. Had a nasty one with DD1, it took a regime of creams to clear up (using what I already had in conjunction with advice from the chemist)
From memory it was a layer of anti fungal cream, covered with Desitin (stinky but oh so good) 2 times a day. The in between changes I would use Bepanthen.

Best to get a medical professional to look at it though. They might be able to prescribe one cream that does it all.