What Causes Sudden Leg Pain And Walking Difficulty In An Athlete?

Hello, I just finished walking the Camino de Santiago in Spain, averaging 15 miles per day for 35 days. It s a 500+ mile pilgrimage, carrying a 20lb backpack. The last 50 miles or so became very painful in the lower part of my leg along the shin. It swelled, but many of us had swelled legs. However, it became bruised and a large lump in the front of my leg and it was painful to point my toes away from my leg. I stopped at pharmacies; once diagnosed with shin splints and once with tendonitis. I ve been a runner most my life and it didn t really feel like either of those. My guess was a stress fracture, but can someone actually get a stress fracture on the front of the leg?? Thanks