hello and welcome,
this is a case of gingival abscess
as per the description given by you.
this is an acute ,localised and painful lesion of sudden onset.
it is caused by sudden forceful penetration of any foreign objects such as a bristle of a toothbrush or an apple core,which carry bacteria deep into the gingival tissue.
it is usually limited to marginal gingiva.
initially it appears as reddish swelling with a smooth and shiny surface.
within hours,it becomes fluctuant and exhibits pointing and through which pus discharges.
the connective tissue
show vascular engorgemant,edema and formation of abscess cavity surrounded by a diffused collection of polymorphonuclear leukocytes
..spontaneous rupture is common.
the invading foreign material,if any,will be usually expelled along with the pus.
visit your dentist
and get a thorough check-up.get your teeth cleaned professionally.
maintain good oral hygiene
.use soft-bristled tooth-brush and dental floss to clean your teeth.