It might be your glands, Mine does it every now and again.
This is actually more common than you think. Here is why the pain exists:
When you eat something sour your mouth waters. This is saliva being pumped into your mouth by the salivary glands. Two of the main salivary glands, the parotids, are in your cheeks, near the jaw.
The pain is caused by the inability of the glands to discharge the saliva they are producing quickly enough.
This is most likely to be due to over production of saliva or by slight narrowing of the salivary ducts. Bottom line... No worries