Hello there ,
Thanks for writing your query,
According to your history i can suspect some remnant of the infected pulp tissue has left unexplored during the root canal
procedure or there is a missed canal due to which the infection has gone worse and you have developed a periodontal abscess
due to spread of infection to the underlying tissues.
This type of periodontal abscess drains in the oral cavity and may lead to nausea and vomiting
This type of periodontal abscess needs to be drained and compressed in position and then followed by a course of antibiotic and analgesic
will subside the symptoms of pain and swelling.
once the abscess is drained the infected tooth needs to be explored again for root canal procedure.
you need to get an x ray done the affected area to confirm the presence of infection,
exact diagnosis can be made only after clinical examination and evaluation by taking radiographs.
so please consider getting the treatment done by consulting a dentist
i hope this helps ,