Sheena, I was going to give the same advice as Andrea...get a t-shirt. My favorite is the "I have autism, what's your excuse" simply because it takes a poke at rude people who stare and judge. Not very grown-up of me, perhaps, but still.... You ARE doing a great job and you are definitely NOT alone. It might help for you to read my essay here
Also, I don't know where you are, but most states have some sort of respite care program. These provide trained sitters to stay with your special-needs child to give you a break periodically. You might want to see if such a service is available in your area. EVERYBODY needs a break. Even God took a day off after creating the world!
You're in the thick of it now. Things WILL get better. I think watching Temple Grandin
, the recent movie, really helped me put the childhood experience into perspective. When you consider how severe Temple was when she was little and how far she's come now, it helps. Well, it helped me.
Big cyber-hugs to you!