Dog is older, large, shivering, lethargic, won't eat, drank a little water, won't get up and walk around - hasn't been outside all day...started about 5pm last night.

Optional Information:
Age: >12; Male; Breed: Lab mix

Already Tried:
Rocky has some existing conditions....he has hip degeneration (can't think of the medical term), and is on a rice, chicken, vegetable diet. He also has acid reflux that we have under control with a daily dose of pepcid. He also takes deramaxx, 100mg 1x/day, fish oil, and 25mg benedryl/day - he has allergies and generates quite a bit of mucuous. Lately, his breathing is becoming more labored as he becomes active - can't walk as far without becoming out of breath...so we stop & rest. Starting around 5pm yesterday, he didn't want to eat (ususally a good eater) and became lethargic. Wouldn't get up this AM to go out or eat. I have been giving him 1 bottle of Ensure Plus to help him maintain his weight...although he eats well his weight seems to be slowly declining. When he wouldn't eat this morning I offered him the ensure and he drank about a quarter of the bottle...drank water and laid down. Has refused to get up since and hasn't been out to relieve himself all day. It is after 4pm and he still won't get up for any of his favorite things or eat anything. He shakes a little when he sits with his head up and is very lethargic. He seems to be feeling very weak, though not throwing up...I'm more concerned because of his lack of urinating. Any suggestions?   It's a holiday weekend so my vet isn't in until Monday.