I really need help getting rid of my lisp, it's ruining my self confidence. Help?

I have had a speech impedement my whole life. i couldn't really talk somewhat clearly until i was five. I have trouble saying words like world (comes out as wer-uhld), and my S's are spread out ("this" sounds like "thiss). My S's and R's are screwed up. I hate it and it's ruining my life. I'm 17 and i went to therapy for it when i was younger. I hate having it and I NEED to get rid of this lisp. Anything you can do to help me would be appreciated so much.