Sounds to me like you have an injury (someone else will likely be able to do better on that) which pizzled a nerve. I understand this is more common in women because we have a tighter calf area; I find that same red area extremely tender to pressure and when I warn masseurs about it they always say, "That's because there is a nerve right there."
MR Imaging of Entrapment Neuropathies of the Lower Extremity
Sural nerve - Wikipedia, the free encyclopedia
Remember your RICE:
and, if not counter-indicated, noninflammatory