As for the diper rash it could be a yeast infection, you would want to see the doc for that. As for now just keep treating it with balmex, or desiten.
As for the bowel movements thats normal really, my baby thats 2 months has 9-12 a day. Babys seem to eat alot and the digest it at different times. Its not uncommon but if you wanted you could if your not already feed him baby cereal, and I think some juices but not too much and ohhh... I know that when I was a baby I constently had a rash from juice ( i'm alergic to citric acid) that could be what is triggering it try laying back on the juice, try water it down a bit and do only one juice for a week or 2 you will find that some will irritate more then others. I hope that helps a bit. Not sure about if you should change to supreame formula yet ( I breastfeed).