This has been going on for 3 years..... Help..

For the last 3 years or so i have been having suicidal thoughts that are getting worse and worse. Im homeschooled so i can not go to a school counsellor. I've tried plenty of times explaining it to my parents and my older sister but i get the same reply 'Stop being stupid, your fine'. My sister went through the same thing when she was about 15 and my parents would do anything to help and did anything for her but now that i've got it my parents dont bother. They think i make it up. I can not do this anymore.