Keeping my problems private didn't work for me and in part led to my first suicide attempt. It's very important that you find a good therapist. If there isn't a good one at school try to explore other options and look into seeing a psychaitrist. Make sure to talk to your therapist about the problems you have with talking to your parents. Sometimes therapists can educate people who are ignorant of mental illness. Maybe your therapist could have a family meeting with you to educate your parents and to show them that how your are feeling is a serious situation not to be made fun of. Just a suggestion, but I know some people have done these family meetings with spouses or parents and it's helped a lot.