Sudocream is the best for rashes on buttock or his private area. It is super effective. No, it was not because he wore diaper for too long but you need to change it more frequently if you buy cheap ones. Whenever you change the diaper, just wipe the area with wet cloth few passes to remove the urine. Dry him before putting on another diaper.

As for nose block, if you are turning on aircond, it might be wise just to turn it off or just run dry mode with a bit of fan.