Hi.. Can understand your concern.. As per your complain pain and sensitivity during the root canal treatment can be due to persistent infection.. When the infection in tooth is severe and root canal treatment is initiated, the infection does not immediately gets weaned off. Other thing is that as you can still feel pain while cleaning of one of the canals it means that there is still living tissue present there which might be acting as a source of pain and infection.. As the temporary filling is done and the pus formation is still there due to infection it creates pressure inside leading to severe pain.. What you can do is to remove the filling from the tooth using a clean toothpick and the cotton dressing present inside and take a painkiller like Ketorol DT or Tramadol to get relief and can consult your dentist soon so that he can further clean the tooth under local anesthesia. You should not get the final filling part done until you are convinced that you are totally painless. Also ask your dentist to slightly reduce the tooth height to avoid contact with the opposing tooth which can initiate pain. Take a complete course of antibiotics to kick off the infection. Hope your query is solved.. If you find the answer helpful please write a positive review and click on find this answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora