Welcome to HCM.
According to your clinical presentation,you are probably suffering from BARTHOLIN CYST
which is located unilaterally inner side of labium majus. Local discomfort and dyspareunia
(painful coitus) are common symptoms.
It needs surgical treatment
called MARSUPIALISATION ( incision of the cyst and closing like button hole appearance). It is minor operation and recurrence is rare. So consult with your doctor for undergoing this operation.
Be well and tc.