Dull Tooth Pain I Deep Clean My Teeth 4 Weeks Ago. My Tooth Is Irritating & Dull Pain On/off. Why?

I deep clean my teeth 4 weeks ago. My tooth is irritating & dull pain on/off. Why? - dull tooth pain

After a thorough cleaning, my tooth # 2 (one 5mm pocket and had the root canal) is irritating and dull pain on / off but it hurts when I eat. I floss, brush with Sensodyne, rinse with salt water and rinse with chlorhexidine before bedtime. It gets even better. However, back in 1 hours or 2, just a dull pain later. Tooth root canal tooth right = dead? What excites me the tooth? What can I do to solve this problem? THX ...