Every since I have upped my strength training, my lower back is killing me. My guess is it is because of a week core due to my recent pregnancy. Is it normal or should I be worried? I have been doing core work outs as well, should I up it? I am mostly worried because the pain is usually more extreme in the morning and my back is so tight that it is hard to move. It normally goes away after I stretch and warm it up, but sometimes it lingers and shoots pain down my legs. Anyy suggestions?