Kirsty I just googled and found this for you

Treating thrush on a skin rash
You will need to see your doctor to get a special cream for the rash, and sometimes the doctor will also give you a treatment that needs to be taken by mouth to reduce the amount of candida in the gut.

If you are using cloth nappies, change them often and wash using soap powders which are labelled for sensitive skin. Drying them in a tumble dryer, if you have one, may make them softer than drying in the sun. Avoid using plastic pants whenever possible.

Some parents find the following helpful although we know of no research to support the ideas. For washing buttocks - a solution of bicarbonate of soda - 1 teaspoon to 600 mls of water. Use a cup of vinegar in the rinse water when washing nappies.

Hope that helps
Jess