My doctor also said the pain in my lower back when I run might be due to sciatica - swelling of a major nerve that runs from the lower back into the leg. He told me to take ibuprofen
after my workouts if it still bothered me, and I've been doing that off and on. But still, most of the time when I run, I continue to get the dull ache and it usually develops into tenderness in one or both of the testicles. It doesn't matter whether I wear breifs, boxer-briefs, or boxers.