Of course, the first thought that would come to one's mind reading this is depression/anxiety. I realize that you tried the meds, but often the meds are not very effective unless used in conjunction WITH regular therapy. Have you seen a psychiatrist?
Now, of course it is possible that you do have an underlying medical condition. Even if the initial cause was not anxiety, I think that after dealing with these symptoms for so long, you have most likely developed anxiety or depression. Pretty much any person would. And I am speaking from experience, as I am now developing severe anxiety after dealing with a brain tumor for 6 months. I am going to see a psyD to help me figure out which of my symptoms are due to a physical, medical problem (brain tumor and surgery) and which are a result of the anxiety that comes from being sick and recovery.
A psychiatrist would not solve your underlying medical issue, but he would give you tools and possibly meds to cope with the process of figuring out what is wrong. I understand the fear of leaving your home because you are afraid of how tired you will be after. Being sick is a huge physical, mental and emotional drain. A psychiatrist may also be able to tell what type of doctor to see.
Most insurance plans allow you to stay on your parent's plan until you are 26.
This website explains community health centers- http://www.dailyfinance.com/2010/03/23/uninsured-where-you-can-find-medical-help-between-now-and-2014/
http://www.freemedicalsearch.org/sta/oklahoma helps you search for free medical clinics
I know you don't have insurance, but as you know, this won't magically resolve itself. You have to find answers to your medical issues, as well as the psychological impact this has had on you. Once you have a diagnosis, you can probably find a physician or hospital willing to treat you on a sliding scale, or as a charity case. In the mean time consider money spent on doctors as an investment in your quality of life. Clearly, that quality is very poor right now.
Best of luck in finding answers.
What kind of doctor did you see and what tests were run?
Sure, you can read on the internet all sorts of diseases and freak yourself out - but odds of a 20 year old with them - ah, not very high... so you need to get copies of the tests, and see what was found.
Also, look at easier/obvious things like diet and lifestyle for changes so you can make - that can help too.
Have you asked for help from your parents?