Hi there, I'm rather new to martial arts (or any exercise) beyond a year of karate as a child. I'm really enjoying it, but have a question regarding some agitation I'm getting on one side of my lower back. When performing kicks with my left leg, there is a horrible clunking sensation in what feels like the top of my pelvis, at the very bottom of my back. It's not painful, although I am experiencing a little tenderness the next day - and a much lesser feeling of the clunk when I walk with my left leg. Could anyone suggest the cause, or recommend any exercises to build up/placate the area? I appreciate that the description is vague, but it's quite hard to pinpoint the position exactly. I'm nearly 34, and while I'm thin, I spend far too much time behind a desk at work. Thank you for any advice you might be able to offer.