I've had issues occasionally- there's no one cause (GCN did a rather helpful look at
sores a while back). I think most of mine have been either abrasion or shorts causing pimples/spots. I have tried Sudocrem, bought a pot after a forum Dun Run in 2010 was somewhat excruciating. Unfortunately, it made the problem worse. Sudocrem has lots of good properties for treating sores, but it's not a moisturiser- quite the reverse, as medical professionals told me (it set back my recovery). Back in 2015 or so, I bought a tub of
this (unfortunately it only now seems to be available from its native New Zealand-
Wiggle stocked it back then), and it's been a life saver when I've needed it, like on tour a couple of years ago. Consistency much like vaseline, thankfully without the same smell, antibacterial properties, effective at minimising discomfort. You'll probably want one of the many excellent alternatives.
@wafter has nailed the key thing: hygiene down there. That, and moisturising if need be. I got a tub of Neutrogena for tours, E45 or equivalent lotions will do the same job and of course cheaper.