I'm 23 and I had numerous episodes of back pains lasting from a few days to weeks. I've never went to the doctor or seek professional help yet. Whenever I have a back pain episode my pelvis is tilted, as if my left leg is shorter than my right one. This becomes more acute after weight training at the gym or long sessions of sitting down. I don't know if this is caused by a muscular imbalance or that my body learned to sit in that position because it's less painful. I found out that standing up, walking more and, most importantly, sleeping on my back help quicken the healing. I also avoid weight lifting during the episodes, it only makes the situation worse.