Good evening! You may have cavity or reduced layers of normal teeth. Brush your teeth with Oral-B UltraSoft Tooth Brush in circular motion without applying much pressure. If there is cavity kindly consult a dentist and get filled. Thank you.
Kindly get an X-ray done of the tooth having pain. May be you will have to get root canal treatment done followed by a cap/crown. Brush your teeth twice daily using correct brushing technique to maintain your oral hygiene.