Hello and welcome,
Thanks for posting your query.
The swelling under tongue may be due to-
Over-penetration of needle of syringe into gums.
Overdose of local anaesthetic
Overpenetration of files into canals beyond the apex.
I would advice you to visit your dentist
and get a thorough clinical as well as x-ray evaluation done.
Take complete course of antibiotics.
Pulp canals has to be cleaned well and dried.
Pus if present at the periapical area has to be drained completely.
Gargle frequently using warm saline and betadine
Hope this helps.