After going for my 6 month checkup i was told i would need a crown put in a my upper back molar.i was worried as in the past i have had 3 root canals done on this tooth and was now at a point where it was ok no pain at all.he said my filling looked weak and a crown would protect it in the long run.

on the first appointment he prepared my tooth for the crown i left with a temporary filling on the tooth.my appointment was for a weeks time and in that time i had no pain at all.
after going back and having the crown fitted the dentist scraped some filling away from the tooth next to the crowned tooth.and i went on my way.almost straight away there was pain when eating and drinking a cup of tea was complete agony the pain was unbearable and it felt like before when this happened that i needed the root surgery. i went back and he put some fluoride on my tooth but this did not help.i then went back again and he said he would fill the tooth next to the crown to rule this out but when he tapped on my tooth the only one that hurt was the crown.now he says he will do root canal on it which is fine but my worry is that he said he will leave the crown on and just go straight up it.but will that not need a filling?and is it normal to have fillings on a crown because i thought the reason for a crown was to protect the tooth underneath.it makes sense to me to remove the crown then do the work and then put the crown back in after all i have only had my new crown for a week.
please advise me on this as im really worried that this is not the right way of doing things.