Old Amalgam filling now sensitive. Concerned

I do have an appt with my dentist next week but I am constantly concerned reading about root canals.  I am 34 and the tooth in question is #2 molar with what appears to be two Amalgam fillings that are approx 20yo.  The other day it started to become sensitive to hot/cold.  Not really pain, but certainly uncomfortable.  No problems otherwise.  I am very concerned for my tooth and pocket book, but mostly the tooth...lol..  Is there any quick fast tests to determine if this is possibly an easy fix or if this is a real bad deal for me?  I hear that throbbing pain is typical if a RC is needed but I just don't know.  I do know I don't have anything close to that in terms of pain.  

[Life360]

Hi and welcome. When the dentist takes an xray he or she will know what the pain is coming from.
If your nerve is being affected then youll most likely need a root canal. Its no big deal but here in the states will cost app $700. They might need to put a crown on it also and is app $1500 for the both.
More often than not the dentist will advise a root canal but you can ask if its necessary and  most likely is because if the pain is from the root, it has been distressed with an infection.

[fastline]

Everyone is pointing me towards root canal so I am curious if ANY level of sensation at a filling site means root canal?  Everyone uses the word "pain" but I feel it is more "discomfort" not constant, only with hot, cold, or extreme pressure.  

[Life360]

The xray will tell for sure. Ive had dull pain and ended up with a root canal.

[mammo]

Before doing anything try a toothpaste made to help with sensitivity to hot and cold.  Sensodyne is good and so is Arm & Hammer with Oragel.  Just because our teeth become sensitive doesn't mean anything needs to be done.  Try the toothpaste and go from there, I think it will feel a lot better.