hello katie and welcome ,
As you have mentioned its been a year you got your tooth extracted and there is no pain we cannot expect any infection in the area.
i suspect the painless lump seen would be a gingival growth or a bony prominence of alveolar bone left unfiled after extraction.
it can be a gum abscess
or gum boil seen due to trauma or infection .
visit a dentist
and get the clinical examination done , if it is a gum growth it can be surgically excised and the area can be sutured.
If necessary you can get an X ray
examination done for the area which will confirm the underlying cause.
i hope this helps,