If he's still able to walk, it is reasonable to try conservative management (medication and cage rest) to see if his signs improve. Sometimes the pain and weakness is due in part to inflammation around the slipped/bulging disc, so if medications and rest allow that inflammation to subside, he may recover. I usually use pain medication in addition to steroids. What are the names of the meds he is on? However, even if he recovers from this episode, there is a chance he may have recurrent episdoes in the future if that disc flares up again. As long as he remains able to walk, you can try meds and rest again for future episodes as well. The strict cage rest is just as important as the meds in allowing his back to heal. For some reason the forum won't let me space out paragraphs, so I'll write more in a second response...

If your boy gets worse and has even more difficult walking, or especially if he becomes completely unable to walk and just drags his back legs like he's paralyzed, then surgery becomes your best option. If he loses the ability to move his back legs, it becomes an emergency, and you should take him to your vet or an emergency clinic immediately. Do you know if you have an emergency clinic in town with surgeons on call to for situations like this? Back surgery is usually done by board certified surgeons or neurologists, but some very experienced general practitioners may be able to do it too. As long he still has sensation to his back legs, prognosis is usually pretty good for back surgery. However, if he loses sensation, then his chances of recovery get worse - the longer the dog goes without sensation, the worse the prognosis. This is why it's an emergency if he becomes paralyzed. If you have a surgeon/neurologist available within a reasonable distance, I would recommend at least doing a consult with them if you boy isn't improving after a few more days, or if he gets any worse.

No, it would be best not to give him Tylenol or Advil, or any other human pain medications. Tylenol is a possibility if he's in a lot of pain tonight, but Advil is dangerous for dogs and even more so since he is on prednisone. It would be best to wait until tomorrow and see if your vet will give you a prescription pain medicine. Since he is on prednisone, he *can't* have any NSAIDs (aspirin family, including ibuprofen, Rimadyl, Previcox, Deramaxx, or Metacam) because this will greatly increase his risk of getting GI ulcers. When I am treating a case of back pain from a slipped disk, I usually use tramadol as a pain medication in addition to the prednisone. The muscle relaxer Robaxin (methocarbamol) can help too since a component of the back pain is from muscle spasms, just like in people. Ask your vet about these options if your boy is walking ok but is still in pain. The Tylenol dose for dogs is 10 mg/kg every 12 hours, so your boy should only get 100 mg each dose. One possible side effect that dogs can have to Tylenol is dry eye, so I wouldn't recommend it especially given your dog's breed.

Ok, a dog who is truly constipated will usually strain and try to go. It is possible that your dog is not going because it hurts to get into position. He may also not have as much stool as he normally would since he is eating less than normal. I would try to encourage his water intake to make sure his stool is not too hard, and he should go when he needs to. You can try adding a little chicken broth to his water to get him to drink more. Feeding canned food will also increase water intake, and you can also add water to either canned or dry food. I wouldn't worry about him not defecating unless he is straining and unable to go.