In my experience, the very first order of business is to make sure your bicycle fits. Then make sure your bib/shorts fits snugly too, as the chamois running loose is gonna rub raw after some substantial mileage. If all that is taken care of, and the issue still persists, then you need to embark on saddle trials. This is taking for granted that personal hygiene is spot on. After my rides, I am in the shower in about five minutes max. And no matter how short the ride, the bib gets washed before using again.

Good luck!