Perhaps it could be caused by one of several things. Anything from insufficient calcium, magnesium, or vitamin c, or perhaps there might be decay in those teeth? I guess you still have the amalgams. Decay can sometimes occur beneath old mecury fillings if there is border separation. Quite often if there is dacay beneath a large mercury filling it can't even be seen on an Xray. I had 25 mercury fillings replaced. Some had decay beneath them. Are you planning to have these large fillings in the rear teeth replaced with porcelain inlays, onlays, or crowns? They are more expensive than composite fillings but are much more suitable for large fillings in rear teeth and would probably last much longer. Inlays or onlays are less destructive to the tooth than a crown, but can only be used if enough of the tooth is present.I hope you have those teeth repaired soon, as it if there is decay there it would not be a good idea to let it progress until you need a root canal(I had one of those. It wasn't fun).

I don't want to panic you, but it should be taken care of ASAP. It might just be a reaction to the mercury though, but why take a chance that it isn't? I had plenty of weird pains in my teeth for years and the dentist kept telling me they were okay. When they were replaced years later there was decay beneath some of them.

How old are these fillings? The older they are the more likely that there might be dacay under them. Most of my mercury fillings were over 20 years old.