@neozcne
i’m no vet at ALL, so take my words as nothing more than an opinion — it sounds like it could be IVDD, especially with the stiffness/whimpering. i worked in a rescue facility for awhile, and we had quite a few dogs in for back leg and paralysis issues.
i will also definitely recommend some sort of cover for his hind paws if he does try to move/pull himself around. when my mom’s pug did in the very beginning, he really scraped the top of his paws up resulting in frequent sores.
gosh, these little dogs love to give us absolute heart attacks.