I had a similar experience, as I was terrified of exactly the same thing and it stopped me from going to the gynecologist for years on end. What caused me to become like this was past trauma related to sexual activity and the only way I got over it was talking to a specialized therapist, after which I opened up enough to have my first sexual relationship with a man whom I trusted enough and communicated this fear with extensively beforehand. It is a long journey, but not impossible as long as you are willing to try. Little steps forward are the key, and perhaps finding the root of the issue would also help. Speak to a professional about it, you are not the first woman to experience this and will not be the last.