I have so many medical issues, what have I done wrong?

First of all, you have done nothing wrong. Many times the illnesses we see have nothing to do with actions or choices we have made, especially as such young people.
   Your constellation of problems suggests that you have one disease which manifests in a variety of problems.  Please ask your primary care physician whether you should be evaluated by an immunologist or a pediatric internist for Systemic Lupus Erythematosus.   The best way to manage a patient who still has college and her young life ahead, is to firm up a diagnosis rather than treating these as isolated other issues, and to gather a multidisciplinary team.  One physician monitors the general systemic issues, and other discipline considers where you are educationally, and another considers your psychologic adjustment through your teen years. Another looks atthe neurologic aspects, and a dermatologist might be a good idea too.   One or two gatherings of a multi-disciplinary team of which I have spoken can make a big difference in terms of the next few years of your life being more comfortable and your being more confident about the future.  It can be managed.
    Best wishes.