Poor little mite I'd take him back to get it checked out. I'll come back on tomorrow with them names of couple of products I used when my DS had a red raw bottom from teething. I still use them every now and then if DS gets a case of diahorrea.
Definitely continue with the hydrozole as it will fight any fungal infection but these will just make it easier to clean him and make it less painful for him.

Also have a look out for Burt Bees Daiper Ointment (I know I know sounds American) but OMG it is sooooo good. It will literally heal a raw bottom overnight. It's pricey at $20 a tube but so worth every squeeze. You may need to google suppliers as they are not sold everywhere.