Thanks for asking the query,
is usually due to gingvitis which is associated with many factors,like plague and calculus deposition, poor oral hygiene
, nutritional deficiencies, endrocrine changes like pregnancy
, puberty, systemic conditions like diabetes and leukemia.
Bump behind the teeth can be because of vitamin deficiency
, tobacco use, smoking, low immunity, leukemia, bacterial and viral infections.
Infected tooth may also drain abscess in the gums forming a lump.
A direct examination by a qualified doctor is necessary to narrow down the possibilities.
I suggest you to consult a Dentist
and get the examination done and if necessary get x-ray done .
Hope this helps out.