Thanks for asking the query,
Small lump inside the mouth which is not painful can be a salivary gland
Inflammation of the salivary gland due to bacterial and viral infections can lead to such lesions.
Other than this it can be due to vitamin deficiency
, tobacco use, smoking, low immunity, viral infection like herpes.
Apart from this it can be a cold sore or an ulceration,or even lesion arrising from an infected tooth draining its abscess in the area.
I would suggest you to get a thorough clinical examination done by the Dentist
and if necessary take x-ray.
Avoid eating of hot spicy food for some days.
Maintain a good oral hygiene
Hope this helps out.