My name Alix. I had always run for ever but last year I ran my 1st half marathon, last month my 1st ragnar relay and just complete my 2nd half marathon 2 weeks ago. Because of that I train almost every day and the more I train the more my lower bakc is hurting me. Maybe I don't get the right position. I don't know but I feel worried because I want to train for a full marathon .
I would look at some of the more obvious answers first...changing out your running shoes, considering inserts and so on. It may be due to muscle strain, but also due to leg length difference, hip discrepency, pressure on spinal discs or basically a combination of things that deal with distribution and force of your weight while running. Most likely, a foot imbalance is causing the problem, but it is important to check out all the possibilities. Consider tapering down your training schedule and avoid hills until you have a professional opinion. Also, swimming and cycling might be good cross-training alternatives if it is recommended to reduce the impact on your lower back.