I was feeling tired and have aches and pains for over a year now. There is no good reason the doctors can find. I'm only 29 and they think I'm making it up. What could be wrong?

First of all there is almost always a valid reason for a person feeling sick. I do not represent myself as a doctor, nurse or any type of medical professional although I have had some studies in those areas. Do not rely on my opinion over that of your doctor(s).
A group of symptoms is called a syndrome. Over the last ten years or so, an illness has been proven to exist and they are calling it chronic fatigue syndrome. Call physicians until you find one who A. Will acknowledge the fact that this disease does exist and is not just your imagination B. Has some ideas on how to treat it. There are a variety of new treatments and I cannot vouch for whether or not they work. I would definitely get a second opinion on whatever treatment is suggested simply because it is such a new area of medicine.
You can have the satisfaction of knowing you were right all along about something being wrong. I would also suggest a support group - try MSN for one of several good ones. (you don't have to be using MSN as your ISP to join the support groups). Do not take medical advice from the people in the group. Like me - they are not doctors and can be wrong. The can share their own experiences and frustrations and give you ideas on how to deal with the symptoms.