What I suspect is that you had a stricture developing and your GYN exam turned into a manual stricture dilation. Your symptoms sound very much like people who had forceful digital dilations without sedation. I sure can understand the pain, since there are oodles of sensory nerves in the anal canal.
Doing the self dilation should help keep the stricture from reforming, so that is a good thing. Hope all your treatments help.
I agree that your GYN should have stopped if she felt resistance. You probably needed dilation, but by your GI doc, nt her.
Jan