You are probably experiencing "shin bang". I used to have major issues with shin bang. Usually, it can arise from a number of issues. Skiing technique is probably the biggest cause. If you lean back in your boots when you ski, or are constantly landing jumps/rails backseat, you strain the tendons in your shin as you lean back in your boots. Then, when you lean forward, you feel that familiar, agonizing pain pinpointed on your upper shin. Improving your skiing technique will GREATLY reduce your shin bang. Secondly, its very important to have proper fitting boots. Reducing the amount of "slop" in your boot will keep everything locked in and help the movement that causes shin bang.
For me, it was a combination of improved skiing technique, getting stronger as a I got older, and becoming more informed about boot fitting that helped to kick my shin bang issue. However, I still get it pretty bad after a day or riding a big jump line.
That has been my experience anyway, I'm not sure if that helps at all.
There are some good threads about this, just google "shin bang".
Try coming to the midwest, were rails are made of rust and tetinus, run ins are about as wide as my wrist, and the landings look like the first 15 minutes of Saving Private Ryan