Much sympathy and hugs for 1-3, but I really chimed in to say something about 4. So I have this aunt who developed a serious illness in high school. And she got tested for everything under the sun, but nothing conclusive emerged from this, even though she was chronically exhausted, fainting, and throwing up every day. Eventually her doctor decided it was psychosomatic and told her school that. This created massive problems with getting makeup work and excused absences and so forth. Worse, that diagnosis got passed along also to specialists she went to who contacted the original doctor for records, so they went into testing already expecting not to find anything. It took two years to find a specialist who actually finally isolated the virus responsible (a brand new thing which is now named after my aunt), and necessitated some home schooling just to deal with the school district.

What I'm saying is that you are definitely not overreacting. Once a doctor has decided it's all in her head, he can fuck up your relationship with the school and also your ability to get specialists to really take the problem seriously. Don't be shy about threatening his career and reputation if he starts doing this.