Yeah I agree, this sounds exactly what happens to me when I need a root canal. The tooth almost feels a little loose if I bite down on it. If you are going to get a root canal, check out calcium hydroxide. Here's a good website--the webdesign is terrible, but the information is great.
http://www.mgoldmandds.com/rctchoices.htm

They can use that in the tooth to "clean" it rather than the other stuff that never ever works.

You'll have to find a dentist that knows how to use it though. They need to leave it in the tooth for 4-6 weeks and then place a composite. DO NOT allow the dentist to fill the tooth in 1 visit.

Good luck! I am unfortunate enough to have experienced 4 root canals.