Agree!!! Need to get to the Vet. In a male dog, especially, that can be from any number of things but you do need to get that checked. Could be something from the penis, bladder, prostate, etc. Is the dog neutered?
No, don't just give him an antibiotic.
Good grief! You need to get your dog to a vet as soon as possible. Urinary infections are extremely painful as you may know if you've ever had one yourself. This is more than a simple infection and you need a vet to assess his symptoms. It's possible he may have developed bladder stones which can be fatal if not removed. Please make that call now!