Throbbing pain after root canal normal? No prior pain before procedure or after 1st session. Only after 2nd session discomfort 2 days. What to do?

Inflammation ? After the second visit, the bone at the tip of the tooth may have become inflamed. There is also a very small chance there is a minor infection. Have your dentist evaluate the tooth.
Call. Call your Dentist or Endodontist (root canal specialist), whoever did your root canal treatment, and report your distress. There are solutions, so call now.