my shoulder is sore... must be cx season

Walking to work this morning, I put my bag on my right shoulder.  Oof, there's a bruise there.  Last weekend, we were only off once per lap.  This weekend was the hometown races - Charm City Cross - just 1.3 miles from my house.  Two races. 6 laps of pre-riding.  Off 4 times per lap most laps (I rode the sand pits a couple of times).  Full on shouldering for the run up, the sand, and occasionally the railroad ties = lotsa bouncing frame on shoulder action.