I am so sorry about
the canals and your symptoms. You're definitely in a tough spot. I'll share my opinion but it's just that--I'm not a dental or lyme specialist.
I know you've spent a LOT of money but there is absolutely nothing more important than your health and I challenge you to think ahead 10 yrs an imagine how healthy you think you'll be if you haven't successfully addressed the root canal issue.
Also, 4 canals gone bad is a pattern. There is simply no way for the tooth or the area to be effectively sterilized, which is the one main fault of root canals--regardless of who you are or who is performing it. There is a high risk of the bacteria getting into the jaw bone, a disease that then destroys all of your teeth. You probably already know all this.
I think you'd be better served by talking with a biological dentist about
alternatives to the root canals being redone. I can't speak in detail regarding those options are but I bet there is info out there and better alternatives available than returning to your dentist and paying him more money to basically recreate the issue. Some people will tell you that a root canal is a root canal is a root canal. The more modern methodologies are better, for sure. But the canal is trapping the bacteria, period.
A hundred years ago I temp'd for an oral surgeon who was a friend of the family and witnessed implants being installed (it's a sight that one can never forget...) Cavitations can go deep and anytime you start digging around, the bacteria has a chance to spread. However, if done by a top notch oral surgeon in healthy bone, the implants might be a good option.
This also might be a good resource--a book called Cure Tooth Decay. It is for general dental care and cavitation care and root canal prevention but I think there was some info regarding root canals I'll share:www.curetoothdecay.com/root_canal.htm
In answer to your questions --
I think you're experiencing worsening symptoms when the cavity is closed up because there is nowhere else for the bacteria to go but further into your tissues. When the filling is removed, there is nothing for your body to react to--either because of the bacteria or because your immune system is reactive to it or to the permanent sealant used.
The tie to lyme is a bit more complicated. I know that the issues that bad canals create are very similar to lyme issues but I wonder if the type of dental bacteria involved are also not similar to the spirochete and that might be the connection, rather than the borrelia preferring detail tissue... I really have no idea but maybe the important point is that the specific abx aside, the holistic approach of lyme & co treatment might also help you recover from your symptoms from these canals (microbial treatment, detoxing, immune support, diet, etc...)
ETA: Here is a mercola article--I like most of his info but not always, so read with an
Hope you get some good info here -