After I clean my carpet it looks great but within a week the dirty areas reappear Why and What can I do?

Have them professionally cleaned. If the spots are reappearing then obviously the cleaner that you are using is not FULLY cleaning the carpets, only the surface. If a professional cleaning doesn't help then most likely you would need to have them replaced. Also, when you have them professionally cleaned, inform them that you are having this problem and there might be a different method for them to clean them. Also, when they are professionally cleaned, ask them to scotch guard the carpets or use a stain guard service if they offer one. This will help with future stain problems and hopefully you won't have to go through this again.