We dealt with yeast when Kenny was only weeks old. Here is what I did:
I began taking acidophilus and garlic. Acidophilus replaces friendly bacteria and garlic discourages yeast (plus babies tend to like your bm better).
Add GSE (Grapefruit Seed Extract) to you diaper wipes solution. If you use commercial wipes, fix up a squirt bottle of GSE with distilled water to use each diaper change. This is VERY drying, but that is good . . . yeast thrive in a moist environment.
Try to do as little 'diaper' time as possible (this would be disposables or cloth - no difference) . . . it encourages the skin to breathe - which it needs to do to heal.
Do not use a barrier ointment - again yeast thrive in moisture and it is ineffective.
Also, we used a paste of Acidophilus (if you buy the capsules for yourself to take you can open about 2 or 3 of them up) mixed with distilled water. It will look like glue and is a bit runny. Apply this to baby's bum before a nap and bed-time (2x a day is good). This will help heal as well.Here
is Dr. Jay Gordon's information on Identifying and Treating Yeast.