No one believes I have a mental illness!

I hate it when I tell people I have a mental illness and they don’t believe me. I told one of my few friends I have bipolar disorder and she said she didn’t think so because I wasn’t abused or had a close relative die. And my parents say it’s normal for teens to have mood swings and that nothing is abnormal even though my therapist speculates I’m bipolar and I used to be suicidal and then later be completely on top of the world. I even had a hallucination last month. I’ll be manic for a week or so, extremely happy and creative but then I’ll fall in depression, thinking no one cares and not wanting to do much. If my doctor said I had cancer, would you say “o no, you just have a cold”? It’s the same with bipolar, they’ll say it’s teen mood swings but really it’s an illness. I’m just so mad and depressed right now that no one takes my illness seriously. My doctor is the only one who gets it.