This problem is known as vaginismus in case there is no abnormality in vagina etc.... u need to visit a gynaecologist for examination and further advice according to the problem.... there are many treatment options available for avoiding the tightening of muscles. Plz book an appointment and visit at the clinic. Dont feel shy or guilty... This is like any other problem e.g. Headache, stomach ache... Everyone visits a doctor for those problems too