What is wrong with me?

So for the past couple of days my mouth has been hurting way back in the back. I thought that it would go away but today it seemed a lot worse. By the end of the day I could barely eat and my face looked a little swollen on that side. So at 8:40 I decided to go to the urgent care. It closed at 9pm. They were nice enough to take me at closing time and so I saw the doctor. He took one look in my mouth and said " wow, you have a very big canker sore in there." That's it, I have a canker sore? I cannot believe something so trivial as that is causing me so much pain. He did say that it must hurt pretty bad and that made me feel better about it. I can handle pain pretty good but this is so irritating. I think the worst part is that it hurts so much to eat. So, he gave me some antibiotics, told me to swish with salt water as often as I can, and to take some advil and it should get better. I sure hope it does because this is getting really irritating. I was secretly hoping for something a little more real to be wrong so that I could maybe take a sick day in bed and not feel guilty but I guess I should be happy I am really fine. Just a stupid canker sore!