I'm 18 I've struggled with depression since 11 I'm always tired and sad, I have so much to be happy about, why can't I feel it! What can I do?

Could be chemical. You are a good candidate for a chat with a psychiatrist. Especially if you have a family history of depression, this could be a chemical thing that's not your fault but may need a medication to resolve.
As above . U became depressed at age 11 , mood symptoms at an early age can be actually bad , which is a condition. That can be misdiagnosed resulting in receiving the wrong treatment for 10 years . U need to see a good psychiatrist. For evaluation and work up.