Not to scare you but I would be very careful with an appendicitis. Here is my quick story: I was having the most unbelievable stomach pains and went to the doctor. The pain had not localized to my lower right quandrant and my white blood cell count was not elevated so they sent me home with some antibiotics. Two days later I still in unbelivable pain and went back to the doctors. By now the pain had localized to my lower right side and my white blood cells had spiked and my fever was at 104. I was rushed to the hopital for emergency surgery. It appears that on the way to the hospital my appendix burst and it nearly killed me. I spent 3 weeks in the hospital while the doctors tried to get the infection under control and lost 30 lbs.
I guess the simple moral is get a firm opinion and if it needs to come out get it out. I think a burst appendix is very rare and im sure the diagnotics are much better today (mine was in '92) but i still would not mess around. My recovery was very long (3-4 months) because of the weight loss. I dont think that you will be running a half marathon in Dec. The surgery cuts through your abdominal muscles and rushing the recovery can cause a hernia. It takes several months to heal completely. If you had the surgery now you should be back training in a few weeks and back to full speed probably by March.