Thank you for your question and I'm very sorry to hear about your situation. Dealing with fighting cancer is enough without having to deal with an uncaring employer too!
Cancer is a disability under the ADA
when it or its side effects substantially limit(s) one or more of a person's major life activities.
In regard to your request for FMLA, you do not have a private cause of action (you can't sue) for their violation. Rather, you will need to report the violation to US Department of Labor Wage
and Hour Division for enforcement. See: http://www.dol.gov/whd/
In regard to the failure of your employer to provide you with the reasonable accommodations you have requested, you may file an EEOC
claim for retaliation
and discrimination. You should not have been written up for absences based on your disability related illness. You file an EEOC claim at the local EEOC office. You'll need to call them to make an appointment.
Finally, regarding the HIPAA issue. HIPAA prohibits the unauthorized disclosure of private medical information. The school asking you to go see a doctor to assess your continued teaching abilities is probably not going to qualify as a HIPAA violation because it is not actual medical information that is being posted. That's not to say that the administration's posting was not rude and potentially defamatory, it definitely was. Nevertheless, there is no claim you could currently make on this posted statement at this time.
Please let me know if there is anything else I can do for you or if you have any other questions. Please also remember to rate my answer positively so that I am compensated by the website for my work. I hope this has helped you.