Dentist says I need a root canal just 3 months after my new crown was placed. I feel he screwed this one up! Is this normal?

#14 had 2 fillings. Tooth crowned mid Feb. I was fine for a week. Then cold/pressure sensitivity and sore spot near the gum line. I've had 3 bite adjustments and last one he sanded a different toot. Normal? The slick texture is gone and almost all ridges have been filed away. I feel he has compromised the integrity of my crown. Is it possible he's recommending a root canal because he doesn't want to replace it? Could it be exposed nerve from an ill fitted crown? Will a root canal weaken it?