Thanks for the query.
The persons with intrauterine devices are more prone for pelvic inflammatory disease
According to your description there is possibility of labial infection
along with PID.
Itch-scratch-infection cycle can lead to labial infection.
So you continue the tablets given by your doctor possibly they will work for labial infection also.
If the swelling increases or persists even after taking the medicines better to consult gynecologist once.