I second the taking away all fruit as it is sugar and also the probiotic. Here are a few other things that worked for us:
-cloth diapers - he could be reacting now to the chemicals in the diapers or at least change to 7th Generation.
-cloth wipes - same reason
-if you are still BFing, remember that your milk contains the sugars that you have eaten, so you have to go on a no sugar diet too until it's gone.
-don't use diaper creams they just hold it in.
-and my best one...Grapefruit Seed Extract (GSE)! It's amazing! When my dd had a mild case of thrush and even the nystatin didn't work, GSE was great. We used it all the time for her diaper change as she was prone to infections. Just mix 30 drops with 8 ozs of DISTILLED water (if you use tap, it will use all of it's good qualities cleaning the water) in a spray bottle. Give him a few sprays every diaper change and nothing else and you should see some great improvements quickly. You can get GSE at Fruitful Yield and probably Whole Foods. We are still using a 4 oz bottle 5 yrs later. This stuff really, really lasts and works fantastic on tons of stuff.
H.