u have gone through root canal treatment that does not mean all the pulp tissue(nerve) is been removed. there is a high possibility of remaining pulp tissue.
the other chances may be iatrogenic errors done during the procedure like perforation, over obturation,
there may be a periodontal problem also.
accoring to me visit another dentist better one endodontist near by u

Thanks for your query, I have gone through your query.
You are absolutely right, a tooth without nerves cannot hurt, but the features what you are giving looks like you are having a gum infection. The supporting structures of the teeth will have nerve supply, So pockets around the tooth secondary to the deposits can cause gum infection, this can lead to pain on pressure or biting. The other possible cause can be a failed root canal treatment. So consult a oral pysician and get it evaluated. If it is gum infection, get the teeth cleaned by scaling and root planing. If it is a failed root canal treatment, then the root canal treatment has to be repeated.
I hope my answer will help you, take care.