After a clean bill of health at the vets...and you can be taught a way to check for a blockage (at least with males)...probably best done in person by the vet....think if there is anything different/strange/upsetting in your life right now. Maybe he is reacting to something, and now is in a pattern??? I think retraining is always helpful with a cat (or dog or child)...maybe a week of a dog crate with the box in there? Or locking your room? Are you washing away as much of the scent as you can? I have heard good things about the spray (feliway, I think).

There is a reason it is happening, most likely, and you just have to figure it out. There is supposed to be some theory behind putting the food on the bed...he won't go where he eats. I don't know if that really works. Stick with it! and good luck.