Oh boy, I thought I had it bad! I feel your pain. Although I have to question the wisdom of the vet prescribing Valium in this situation since it's actually an appetite stimulant.
How much exercise does Otis get? Do you think if you were to tire him out (or as much as would be considered safe for a 13 yr old) with a boisterous play session just before bed, that might help?
Instead of the pheromone collar, you could try a Feliway pheromone diffuser or 2 around the house.
I'm not usually a fan of adversives, but you might have to resort to something like SSSCat Cat Repellant
for the time being. It emits a pssst of air when a cat enters within the range of the motion detector, scaring (but otherwise not harming) the cat. You could place one outside your bedroom door when you go to bed.
Perhaps earplugs are an option? That combined with 100% adherence to NOT getting up when Otis cries, no matter how persistent he is, should eventually
extinguish his behaviour. But it takes only one time of giving in to reinforce it exponentially. Kinda like someone playing slots at the casino.
I wish you luck!! 2 of my 4 cats are early risers, and I don't have a bedroom door to close.