My Bearded Dragon has something protruding from his rectum that wont come out, any suggestions of what it is?

We just bought him today from the previous owner. The previous owner said that this is something that has recently occured and he is not sure what it is. We are very concerned that there might be something wrong with him. Our dragon is around 5 years old and seems otherwise very alert and healthy. I am very concerned. Please help!!!!