“Should I be concerned about root canal pain?”

It depends on the tooth. Certain teeth like upper 1st molars sometimes have extra canals that can be missed. You can find out if they treated 3 or 4 canals. If the doctor has a conebeam imaging system they can take a 3D picture of it and see if anything got missed. You may also be hitting a temporary crown of filling too hard which will make the tooth hurt even after Root Canal Therapy is performed. There's also the possibility that the tooth may have a fracture in a root in which case Root Canal Therapy will not work. If it doesn't seem to be getting better I would have the Dentist/Endodontist take a look at it.

You should call your dentist to see if you need antibiotics or if he needs to adjust your bite.

If it’s still hurting after 3 days that is unusual. I also don’t know the severity of your individual condition so it could be normal. It’s just not typical. You should be on antibiotics regardless.
I would contact your endodontist or general dentist who did your root canal for a follow up.
Dr. J

It takes 6-8 weeks to completely heal.

When I had a root canal done most of the pain went away after a couple of days. But the tooth didn’t feel quite right for over seven months. If the root canal was done in the back of the mouth, the infection that gets out into the bone is not cured by having a root canal done. The root canal filling only fixes the cause of the infection, which is the damaged tooth. The infection that gets out in the bone around the end of the root is much more difficult to fix, and your immune system is what fixes it. The immune system works like ants taking away a sand pile, very slowly, because it’s hard to get to infection that’s in the bone. Sometimes it’s many months before the pain is totally gone. Mine has been comfortable now for over 30 years! If your pain gets worse, not gradually better, you need to let your dentist know.

Slight discomfort improving daily is relatively normal. Usually OTC meds (ibuprofen, acetaminophen) helps. If the pain is constant, increasing.

It is normal for a tooth to be a little tender or sore for a few days after a root canal. If it lasts longer than a week, you should go back and have it checked.