I am sorry for what you have been through... There are many reasons for what could have happened wrong. Doctors negligence could be one among many. I also believe doctors being useless who have sold their soul to pharma companies but there is pretty much good percentage of doctors who work upto the mark of Ethical Code of Medicine. Do internet research for them rather looking for some net advice for a sign you observe. As already said, A sign and Symptom can be same for pretty much 10's of diseases and internet (sometimes can co-relate the S/S to correct Dx) can be deceiving in telling you exactly what you have based on just one sign. A single apthous ulcer (heals on its own mostly) will be prompted as Neoplasm coz ulcer occurs in Most Oral Neoplasms as well. So proper Physical Examination and Diagnosis is important which is only possible when you approach a medico who is specialist in that field.
I believe one unethical and Wrong doctor doesn't make all doctors Wrong.
P.S. Doctors are still humans not Gods, prone to make mistakes (not justifying), however, Strive to minimize this mistake rate. My professor used to say "when a doctor makes a mistake, a person dies. Thus strive to minimize it to almost zero."