Slept on a pull out sofa bed now and now I have lower back pain?

On Friday of last week I went on a road trip and was in the car for about 6 hours. That night I slept on a pull out sofa bed and did so again Saturday night. Sunday morning we woke up and I had pain in my lower back only on my right side. We came home that day and were in the car for 6 hours again. Since then, I've had pain in my lower back. It is a dull pain sometimes, and a sharp pain when I bend down to pick things up. Before sleeping on that couch, I didn't do anything out of the ordinary for me and I know I haven't pulled or strained anything because I haven't done any strenuous activity. The pain has been going on now for about a week and isn't getting any better. Does anyone know what this could be or anything I could do to help it? I have been pain over the counter pain medicine and it helps, but it doesn't make the pain completely go away.