Is he straining to urinate with no production?
If you press on the sides of his abdomen is he painful?
What color is the pus from the penis?
If he is straining and there is no production then he needs to be seen tonight. This is usually due to a stone getting stuck in the urethra. There is a bone in the penis of dogs so if they have bladder stones that they attempt to pass, they will get stuck just before reaching the bone as the urethra cannot expand at that point. This is a medical emergency as urinary obstruction can cause kidney failure, bladder rupture and it is extremely painful.
I would get him to an ER vet now so that they can anesthetize him and then flush the stone back into the bladder so the bladder can be emptied. He will then need surgery (which can be done at a later date) to go into the bladder and remove the stones (likely to be multiple stones).
I hope that helps, let me know if you have any other questions.
I wouldn't give him anything- there are no over the counter pain meds that are safe at this point with the kidneys.
I hope he does ok through the night- just be aware that this will kill him if not relieved soon enough. I don't know how large his bladder is and how long he's been obstructed to tell you how much time he has, but just be aware of the potential consequences.