Unexplained Soreness, Tender To Touch, At Lower Left Ribcage, Backside

Unexplained soreness, tender to touch, at lower left ribcage, backside of ribcage -- the floating rib. No injury occurred. After 12 days hiking, I woke up feeling fine, but when dressing felt tender spot. It has endured two wks. Not sure if xray will reveal cause, as it seems more tissue than bone. Never experienced this before. Health is excellent overall.