sister, you have to be more assertive about your identity and freedom of religion. It is discriminatory and a violation of your human rights to terminate your employment because of hijab. File a complaint. This is the 21st century for goodness sake! Everyone has a right to wear what they choose to.
You can wear a bonnet or some kind of hat while you are at the hospital once you are a medical student. They can't argue with that. They won't. Not if you show them that it does not interfere with your ability to be a doctor.
Don't let shaytan (the devil) shake your self-confidence. There are all sort of obstacles that all people face. But there are certain things that you cannot compromise on or apologize for.
Be strong, and don't dwell on what other people say, whether they are muslim or not. Wearing hijab was a good choice that you made. Don't second guess yourself. Things will turn around insha'Allah. May Allah give you the strength to continue wearing it.