Stretches/Excersises for lower back pain while running

Hey,

Preseason rugby training just started so we have begun by doing alot of running! For the summer Ive been doing alot of cycling and weight lifting but I havent been doing any running what so ever.

Now a few minutes into training my lower back gets increadibly sore, I feel like an oul fella (im 21) and its very tough to keep going. So I've decided that when in the gym I'm going to focus more on abs and lower back and before training I'm going to to do various stretches and overhead lunges.

Has anyone else experienced this? I read its pretty common. What has worked for you?