Dear Liza,
I would suggest that your find some information on the Internet to show your parents - let them read what you have found, and explain how you're feeling. I wasn't diagnosed with Asperger's Syndrome until later on in life. The symptoms can go unnoticed to those who don't know about it. My family just thought that my problems were something I would just grow out of. I understand how you feel, that knowing would make life so much easier, and I hope that it will be easier for you, once you know for sure.
You could try this test:
http://www.piepalace.ca/blog/asperger-test-aq-test/ But, remember, you will need to speak to a doctor, who will probably refer you to someone who can test you properly for Asperger's.
Take care of yourself.
Halcyon