Back injury while biking??? This might sound strange, but it keeps happening to me, and I don't understand it. I'm on my 3rd one right now and I'd like to keep it from happening again.

The first time, I was at a stop and was in a hurry to cross an intersection, so I stood up and pressed hard on the pedals to get going, and BANG! I felt a sharp pain all over my back! It got worse and so painful that I could hardly walk afterwards. I think it took several days to get better.

The second time, I was on a casual ride to a fast-food place (Arby's) a couple miles from home. It was shortly before I got there that I started feeling a slight pain in my back. I got off my bike and went in and got my food as the pain gradually got worse. On my way home, it continued to get worse to where I was wondering if I'd ever make it. When I got home, I just laid on the floor. It's all I could do. But the time came when I had to go to my job, but there was no way I could. I ended up slithering over to my phone and calling in telling them about my problem that I couldn't work that day. I couldn't even get off the floor. But about an hour later, it went away about as gradually as it started. I was shocked it went away within a few hours from start to finish. I still missed that day of work.

The third time was a few days ago. I was on another casual ride when pain in my back started gradually. It gave me flashbacks to the second time, which was about 10 years ago. It didn't get as bad, but it hasn't gone away yet either. It remains in the lower right side of my back and bothers me a lot when trying to sleep, so I have to lay in a certain way on my side and try not to move. It's been about 3 days like this without improvement.

So now to my question. Since this happens only while biking, whether aggressively like the first time or casually like the other 2 times, can someone please tell me what I could possibly be doing wrong that would cause this to happen? Has anyone else experienced something similar?