I looked in the mirror and was fine. about 10 minutes later, i looked in the mirror and saw that my left jaw was swollen in front of and under the ear. there was no pain. moved to neck overnight/turned red. sore. now, 2 days later, almost gone?

Glad to hear that this swelling is going away. The area in front of/under the ears typically contains a line of lymph nodes. It is possible that you had some kind of mild infection which caused your lymph nodes to react and enlarge. Try to recall any symptoms that you had in addition to this. Sore throat, ear pain, sinus pressure. If it occurs again, see a Dr for full evaluation.