Welcome to the boards!

It's not a very good idea to lock your dog in the bathroom as punishment. Dogs don't reason like we do. They don't know what's right or wrong according to our standards. Your dog won't understand that his pooping caused you to lock him in the bathroom and so, therefore, pooping must be bad. He just won't make that complex connection, so I would stop locking him in the bathroom.

First, my advice to housetraining lapses is always to check out your dog medically and make sure he's physically sound. Make sure he doesn't have a UTI or GI problems.

Next, since you say there hasn't been any dramatic changes in life, has there been any changes at all with the placement of the newspaper?

If that's not the case, I would simply start back at Square 1. A lot of dogs like to eliminate on soft surfaces, so that could explain why yours chose to go on your bed (it's actually pretty common ). For now, treat him like a puppy and restrict his access to the bedroom. Take him to his newspaper every few hours and supervise him constantly or crate/confine him. Hopefully, you'll only have to re-train him once!