Hello & welcome,
Your molar tooth which was previously restored seems to have developed periapical abscess
, that's why you are seeing hard lump on the gingiva
related to same tooth.
Now, the swelling or lump is hard & here is the clue. You have taken antibiotics for prolonged period i guess without draining that infection in the molar. Probably this caused the abscess to indurate & thereby Antibioma has been formed.
First off all, stop the intake of Antibiotics and visit your nearest dentist
to clinically evaluate the tooth & swelling. Dentist will then make straight line access to pulp chamber to drain the periapical infection in the tooth.
Use of Antibiotics will be decided by your dentist only.
X-ray has to be taken to know the periapical condition of the tooth. If dentist feels its ok, then yes, you will have to undergo Root canal treatment
If you can not afford the Root canal Treatment, then extraction will be the only answer.