I had a root canal done 3 weeks ago and a permanent crown placed 5 days ago.

I would recommend returning to your dentist to have the tooth examined. The throbbing pain you are experiencing could be caused by a number of factors, so it's important to return to your dentist for the proper diagnosis. It's possible that the crown is high, and a simple bite adjustment is all you need. Even the smallest high spot on a crown can cause discomfort. I hope this helps.  Follow me for more questions and answers.

There are many reasons why your crown might be throbbing after being normal for 5 days. Without doing an exam it's impossible to give you a diagnosis. I suggest returning to your dentist today and having them check out the area. It might be a minor adjustment of the crown that is needed. Don't jump to the worst conclusions because the cause is probably minor.