christie...Thinker has a good idea, and one we have had to use with our daughter the slob.
As he is under 18 and unable to support himself, take EVERYTHING away. Make him earn things back. One week of showering daily, he gets his laptop (for example) two weeks of making his bed, he gets an air gun.....
Just a thought...my daughter also has "too much" and she only appreciates the things she buys herself, or that she has had to earn. And the stink? Girls can have funky odors too!
She does not have issues like Aspergers to deal with, but if you keep it basic and consistant it shouldn't take too long. I worked for 16 years with people having all types of issues and basic and simple really work the best. Yelling as you know only works when they think you might kick them hard!
I hope things improve for you soon.
