I'm sorry to say that you're wrong. Sherlock never tells John the why because I don't know the why and I have the feeling Sherlock isn't sure either. I have speculated some about how this started over in the comments on AO3, but the only thing I know for sure is that it started when he was 14. Sometimes when I poke at him I get the feeling that his mother had a complicated relationship with food as well and that he once was force fed with a nasogastric tube when he was 17. But that's pure speculations.

The closest to a sequel is the 221 bathroom (http://solrosan.livejournal.com/28789.html) that I apparently haven't put up in the master list. Bad solrosan!