There is a long history of prohibitions against masturbation.
Many of these were health related, they are all false, you won't grow hair, you won't go blind, etc. etc.
There are many people who use pornography as a means of arousal when they perform masturbation. While this is nothing to be concerned about if you become obsessed with masturbation, it is easier to get addicted this way.
Often we believe (for whatever reason)that "normal" sex is with a
committed relationship and limited to specific positions. This is often related to specific religious ideas. There is a reference in Leviticus about seed falling on barren ground.
My ex-wife preferred anal sex, until she discovered it was sodomy
and it was against her religion to practice this. I never enjoyed it much so it didn't bother me. Oral sex can also be prohibited. My ex-wife loved my performing oral sex
on her, but she used religion as a reason to not perform oral sex on me.
Mostly I think the shame comes from a feeling of being inadequate
to get our sexual needs met through a relationship.
The truth is that almost everyone masturbates whether they admit it or not. Men, women, single, or married, gay or straight.
The issue is to identify the source of your shame. MY bet is it is not even your shame, but shame that was transmitted on to you
by others.
I wish you peace, May God bless you and keep you until then.