Hallow Dear,
Tight
cervix is one of the factor of failure of conception. You have to find out how tight is the cervix. Very tight cervix will cause intolerable pain during your
menstruation.
Your question is very valid that if your menstrual discharge can come out how is it that sperms cannot go in.
My dear, during the menstruation, the
uterus is contracting and pushing the lining and the blood out when the cervix will open; while there is no such force for the sperms to get pushed inside the
uterine cavity. The sperms swim their own way through the cervix towards the egg. However, if too much uterine force is required to open the cervix, it will cause considerable pain in lower abdomen and low back ache.
May be the inner lining of the cervix is not conducive for the sperms. This is called as cervical factor which (empirically thought) gets corrected after dilatation of the cervix.
To have the clarification on your doubt, you may undergo
Ultrasonography in which the diameter of the cervical canal and the inner opening can be measured.
I hope this clarifies your doubts. If you want to have further more discussion on this issue, you may ask me Direct Question.
Dr. Nishikant Shrotri