My butt sometimes hurts when I'm having back problems. It also hurts when I fall on it, or when I've been out riding hard. It can be hard to tell the difference. That's because nerves can be affected by the muscles, or affect their muscles causing tenderness or spasms. This could be the type of thing that appears later. I'ld suggest seeing a doctor, tell them what happened, what you've been feeling, and ask them assess your back.