I'm sorry to hear about your problems. You are way too young to be having these symptoms. There are many things to consider here including fibromyalgia, chronic fatigue syndrome, mitral valve prolapse syndrome, depression, and others.
My best advice to you is to get a second opinion from another doctor. If you have gone to multiple doctors in search of an answer, please consider going to a major university medical center like Cleveland Clinic Foundation, Mayo Clinic, Johns Hopkins, etc. and have them see you there. Believe me, sooner or later you may end up getting the wrong treatment if you don't see the right specialist (I would personally suggest seeing a good internist or perhaps a rheumatologist in one of these medical centers). I sincerely hope it works out and that you get properly taken care of.
Vincent Font, M.D., FACP, FCCP, FACC