I think I have a canker sore?

I read about canker sores vs. cold sores, and I believe I have a canker sore. It's on the inside of my bottom lip, looks white, has a bit of a dip in the middle. It's also pretty small, maybe 3mm in diameter. It hurts really badly and my lip is puffy. What can I do about it, and how long will it last? Is there any information you could give me?