Here's a bit of a background:

First noticed a slight pain on the middle molar tooth around the end of January

The pain soon turned to a throbbing pain on that tooth and the gum surrounding swelled a bit; this lasted for a day or two.

Then all of a sudden the pain was pretty much gone and I just waited for the swelling to go away.

For the next week there was no pain--yay!

Then two weeks ago the pain came back but not as bad as it was the first time. It's more of an annoying pain you only feel when you accidently chew with that tooth or put pressure on it. Very cold water tends to stimulate it. Sometimes the pain sorta "lingers" with an annoying effect.

I've come to the realization that I may have a tooth decay. I talked to a friend who experienced this and said something about a root canal thing.

My concerns are that it has beeen a month since I first felt the pain. Can the tooth still be saved? He said a root canal is a process, and it can't be done in one dental visit. Is this true? He also said it's expensive! Please give me more info! I plan to schedule a dentist visit this Monday!