hi and welcome,
swelling and infection is usually not seen on the roof of the mouth. Palatal swelling near the molar area can be due to some infection in the adjacent teeth or periodontal tissue. Infection in the molar or premolar area or formation of abscess either tooth related or periodontal abscess
may drain in the palatal area.
The lump can be cystic as well . Exact diagnosis can be done only after clinical examination.
i suggest you to visit a dentist
and get the clinical evaluation done . you can get an OPG radiograph which shows the extent and severity of the palatal lump accordingly enucleation of the cyst or drainage
can be done. i hope this helps you , take care.