When drinking or eating something sour, once in a while, the area of my jaws closest to my ear stings for a few seconds. Not chronic pain, but has happened all my life. Can someone explain what this is?

Glands. We all have glands in that area called the parotid glands or possibly salivary glands all of which produce essentially saliva. It would not be unusual for someone to have those glands respond to sour tasting foods or drinks to contract and produce saliva. You may have slightly more sensitive glands to the taste of sour.
Sour Power. What your actually experiencing is an instance of glandular contraction, most likely of the parotid glands which reside in front of the ears. The duct for this gland exits in the top part of the mouth, and can be seen as a small bump in the gumline of the mouth. When consuming sour foods you're stimulating release of saliva from this gland, which results in a harmless and unusual sensation.