No pain, but sense of urgency when he lays down?

When my husband lays down he will feel like he needs to go, but when he tries there is nothing there. And it only seems to pop up when he lays down or is sitting in a weird position. He says it doesn't hurt, but it is uncomfortable. The doctor originally thought it was an infection, but no infection was found. They gave him antibiotics anyway and said maybe you do and we just don't see it. Well, those didn't help, and now I'm trying to convince him to go back. Any thoughts on what this might be? After the last doc appt he cut out caffeine and a lot of sugar from his diet, but still same symptoms.