Hello, you have not mentioned when was the rct done. if it was done recently, it might pain for few days but eventually it should become normal. If it was done long time back, and you started feeling pain on chewing now that means you should go for a check up as it might be infected. also get it crowned once it becomes normal as crowning increases the life span of the rc treated tooth.

Sometimes in the starting few hours it may happen, but if pain is in the tooth after a week of a RCT, is a matter of concern.