Lump after first time sex

This is kind of long, but I want to give full details. About 4 days ago I had sex for the first time. The next night I had an almost constant urge to urinate. I would wake up and go to the bathroom, only to just stand there have nothing come out. I drank a large glass of water really fast right before bed, so I thought that was the cause. Well the next night I was talking to my girl and was about to masturbate. It just wouldn't get hard. It was a little firm, but that was it. Yesterday I noticed that there's a lump looking thing on the underside I haven't noticed before. It's not tender to the touch. My penis isn't numb, but when I touch it I don't really feel much. I mean I feel my fingers on it. What is wrong with me? I just had sex for the first time, and this happens? I have been worrying profusely about this... Please help?