Is there anything that can be done to fix a lisp?

I'm seventeen, and recently discovered I lisp my 's' and 'z' sounds. I'm not that talkative anyway, but now I can't stand to listen to my own voice. I can't take myself seriously and can't expect other people to. To make things worse, I've developed a bit of a stammer. I know it's a confidence issue that has sprung up from the lisp, but I'm so embarrassed and frustrated by this, even more so because I can't articulate it! My parents both laugh it off and say it sounds 'cute'. I'm in bits over this. Any advice would be much appreciated, and speech therapy isn't an option for me.