Dear , first thing u should not keep plaster.
As u said it was itching may be because of dryness but then irritated it ,so may be u scratched lead to wound and infection and then u did plaster all those leads into more problems.
First remove plaster clean with water , water u should boil then make it cold then use for washing , keep batadine ointment on it.
Consult gynecologist
Next Steps
consult gynaecologist immediately
Health Tips
avoid self medication &treament ,sorry to say in india doctor fees is very much less than one movie ticket so dont lead your healthy life into trouble with self remedy .