Bit of a shot gun approach here, but you sound desperate. Ignore anything that doesn't apply, sounds stupid or you just don't like the look of. I'm assuming this is soleus muscle rather than shin splints, by the way.
1) You probably overpronate on the relevant leg - check your walking shoes for signs of wear on the front inside edge. If it's there, upgrade to more stable shoes.
2) If you notice this pain when walking as well as running, make a conscious effort to walk with your feet in a straighter line, especially on the relevant foot. I don't suggest trying to adjust gait while running without professional advice.
3) You are almost certainly overtraining. Being seriously competitive does not mean being a nutter. You are getting older and that means you have to take regular rest days. Sometimes the drive can be counter productive in reaching your goals.
This is based on nothing but personal experience. Hope it helps.