The most common problem is "sialoadenitis" where the gland gets blocked up, and becomes painful and swollen.
is a common cause. This can be initially treated with hot compresses, good hydration (lots of water) and sour foods/liquids taken 5-10x/day (vinegar, lemon juice, sour candies, etc). Ask your doctor for details about what he/she thinks the problem is. Best wishes.