Melissa, I am so sorry that you are in such pain and, seemingly, for no reason.
You've got to go back to your doctor (or to another one) and demand that they help you figure out what's going on.
Your symptoms could be attributed to several conditions.
Ask your doctor about rheumatoid arthritis. Symptoms include morning stiffness, joint pain (on both sides of the body), flu-like symptoms and fatigue. Though it typically strikes women older than you, it can affect people in their teens and twenties -- it can even affect small children. You could see a rheumatologist for help diagnosing this (or ruling it out). Visit our Rheumatoid Arthritis site for more information and ask questions of the community there. They can help get you started.
Also, ask your doctor about Lyme Disease. Though it affects a lot of body systems, some symptoms do inclue muscle pain or weakness and extreme fatigue.
You may also want to check out this page on Guides to Chronic Pain conditions. It lists several things that can cause all sorts of pain.
I hope you get the help that you need. Visit again if you have any more questions!