You may be experiencing a valve issue. Of course, it could be any problem. It's really hard to tell with toilets. I would check the water level first and add water into the tank if it looks like it doesn't satisfy it's system. My toilet gives me a lot of trouble and I am constantly calling for plumbing services. However, a lot of times when I'm having issues I'm able to fix it momentarily by adding water or pulling the chain link my self. http://absolutelyclearsewersandplumbing.net/Services