I had a root canal with crown five months ago after gum surgery. Hurting. What could be the problem?

Hi:
Most likely the bite has to be adjusted and make sure there is no grinding or clenching pressure on the crown as well. Also food impaction can cause gum inflammation with translates into pain. Please go back to your dentist right away to check he bite and evaluate the gum.
Best,
Dr. Maddahi

I sounds as if the tissue around your crown is irritated due to the food packing. I suggest returning to your dentist to have it evaluated.