You should try to do some strengthening excercises for your hip flexors. This will take the strain off of your groin and back and allow easy comfortable motion. I would recommend starting on the floor laying on your side supported on your elbow. Slowly do tension side kicks; out 5 seconds as high as you can, then hold it at full extension (or as far as you can get) until you feel a burn in your hip then release and re chamber 5 seconds. Repeat this enough times that you start to fatigue a bit and it gets pretty hard. Do this on both sides. After doing this for a period of time on a regular basis, and it starts to get easy, move to standing up holding onto a wall and doing the same procedure with a full standing side kick (slow motion, just like on the floor) hold out for 5-10 seconds, and rechamber. This will help you strengthen and also pinpoint any problems with technique you may have. It works wonders. Hip flexors are sometimes neglected but are very important to good side kick technique. Try it out. It might fix your problem. -Tom