Hello and welcome to hcm,
The lump can be abscess arised due to gingivitis
or aphthous ulcers
which is recureent in nature.
Get your teeth cleaned and root planning done.
Pus if present has to be drained/curetted.
Take fluids and vit-b12,c ,iron and folic acid rich food.
Maintain good oral hygiene
Steroids can be taken in severe conditions after consulting with your dentist
Hope this helps.