Thanks for using Healthcaremagic,
Your description suggest to be infective in origin which could be bacterial infection to hair root?
As it has ruptured and drained naturally just keep it clean and apply some antibiotic ointment and it should heal.
If pus collects again and increases in size then get it examined and if required antibiotics and anti inflammatory treatment may be given to hasten recovery.
is formed(less likely) some time it needs to be surgically drained.
It is certainly not cervical polyp
as polyp is very deep inside vagina and not visible from out side.
Hope this helps.
Dr.Akhilesh Dubey M.D.