powerstep orthotics are pretty decent, cheap, over the counter orthosis. There is a PTTD brace. Ankle braces can help. Dont go for any injections if that is truely what it is, but it doesn't sound like thats truely your problem. midway between the knee and foot is the Post tib muscle rather than the post tib tendon which is what usually gets inflamed.
RICE therapy works well for PTTD. rest. ice. compression. elevation.