6.5 month Shiba taken up peeing on our bed

I dunno what triggered it. He’s 6.5 months, close to 7, and is taken outside for potty every 4-7 hours depending how active he is. He was potty trained solidly around 4 months and very rarely had pee accidents in the house, and those happen if he drinks a ton of water and we didn’t know it or something.

A month or so ago, he started jumping up on our bed while we were away. I didn’t think it a huge deal since our dogs alternate going in the couch (not allowed). In the past two weeks, he’s peed 5-6 times on our bed and it’s getting ridiculous. He’s punished for it (a few times after the fact - by being brought over to where he peed, have him sniff it without his nose touching, then put into bathroom for his timeout). Today we caught him right as he was doing it and my fiancé punished him again. The problem is, it seems like no matter what we do, he keeps going back and doing the same thing. We’ve washed everything each time (down comforter, duvet cover, sheets) and soaked odor remover into the parts of the mattress that were wet.

What else can we do to stop this behavior? I don’t know if he’s just rebellious as hell or has serious behavior problems when it comes to obedience. He’s my 3rd dog raised, been around lots of family and friend dogs, and I’ve never had so much trouble getting a dog to stop doing something like this. I’d care less if he peed on the damn floor so we didn’t have to spend 2.5 hours washing everything.