My dog has a rash on his underbelly/groin area, what can I do to make it go away?

I have a 7 month old bull terrier. Just this evening I noticed a slight rash that covers most of his underbelly. His tummy isn't all red, just little red bumps scattered on his skin around his genitals and thighs. I've read some articles and have gotten multiple theories. He has this stuffed sheep that he "loves" and I washed it yesterday with the hose and used his shampoo. I know I didn't get all the soap out. He got it back today but when he gets his baths he isn't affected by his soap. We've also changed his food this week. It went from Blue Buffalo to Kibbles n Bits. The only thing that has changed so far is his bowel movements but I understand that is normal when changing foods. I am really stumped as to what my plan of action should be. Do I take his sheep from to see if it clears up or change back his food? Do I put an ointment on it? Should I clean it with rubbing alcohol?