What is Causing One of My Teeth to Feel Like It's Hitting a Nerve When I Floss?

It's been like this for the past 6 months and the dental hygienist said she doesn't know any reason for it and the dentist didn't see anything wrong with the tooth in an xray. It's the surface of the tooth (not the gums) which is sensitive during flossing and the tooth is tight, right next to a crown, if that makes any difference.

Mabey its youre wisdom teeth or u neegd a rootcanale or cavitys