Zingers pain @ three weeks post whitening

I’ve had sensitive teeth for years and recession on two lower front teeth. All noted in my records but no one warned me about pain from opakescence 20% gel to ready teeth befire replace two crowns on the top. Pain started days after I stopped bleaching. (Only 5 Times. Only half the amount of gel in trays) I’ve had gluma (1x), Seal & Protect (2x) and this week, composites on exposed roots (2 days relief).Yesterday it started again. I’m terrified . Root canal? What can be done?