I've had root canal on my molar 6 days ago. i went back for 2nd session but still painful sodentist says come back after 5 days. i still feel slight pain.

Healing: As long as the discomfort is getting less then that is a good sign. Make sure that the dentist is checking for any infection or issues with your bite that could contribute to pain also. Root canal discomfort can linger until everything heals. The discomfort should be very minimal when the procedure is completed.

Multiple reasons: Some pain after root canal treatment is normal. If your dentist does root canal in multiple visits, it is possible all the diseased pulp tissue was not removed after visit 1. After the final visit , pain may persist for a while, depending on many factors. If the pain is getting worse, call your dentist and get in sooner. If you don't get an adequet explanation, get a second opinion from an endodo.

Check your bite: Post endodontic pain frequently is related to the contact of the treated tooth to the tooth in the opposing arch. If the treated tooth is touching the opposing tooth when you close your mouth it can be easily adjusted and relief may spontaneously occur. Treatment causes temporary swelling of the ligaments that hold the tooth. Adjusting the bite provides time for this swelling to subside.