Multiple visits. Root canals can be tricky and often require more than 1 appointment when infection is present in the tooth. A typical root canal takes 1-2 visits, but 4 is not unheard of. If you are seeing a skilled dentist/endodontist, they may be ensuring that the infection is completely under control before finalizing the root canal. When you go in, ask why so many trips.
No! Not normal. Most root canals are completed in 1-2 visits. Yours is obviously difficult or presents some complication. You are lucky your dentist is conscientious enough to spend 4 visits treating you for a procedure he likely only expected to spend 1-2 visits on. He/she seems to be trying to do the best job possible, while frustrating for both of you, you will be the beneficiary via the best poss. Outcome.