I don't think anyone but a trained psychiatrist or perhaps, a psychologist could say what all is going on with your partner. It certainly sounds like there are "control" issues going on. There is a lot of basic information online for sexual addiction and bipolar disorder. You could scan through some articles just to get a basic understanding of common symptoms...but it is a tricky area as many of the "personality" disorders share some common behaviors.
There are some common symptoms of bipolar disorder that are used for diagnosis. I think it is OK to post this from HealthBoards' sister site:
It seems to me that he is clearly self-centered and looks at the whole world from that position. I have a close family member who is bipolar. It is typical behavior to believe that what he(the person with bipolar disorder) believes (whatever the topic) is the only way it could be...and there is a genuine surprise and disbelief when it is pointed out that others might feel differently. Of course, HE is correct, and everyone else is wrong. To us this would seem illogical, but to that person, it makes no difference if all people think differently or know something to be true -- if he feels otherwise, he is correct.
As I understand it, people with a true sexual addiction have other behaviors as well, such as having multiple partners because one person cannot satisfy the "addicted" person; watching porn; masturbating; generally just engaging in activities concerning sex, thinking about sex, etc. all the time.
From your description, it seems that your partner has no regard for how you feel about the relationship, or for your needs or wishes. Whether the guy is just a louse or has some serious personality disorders, it sounds like he is unlikely to seek help....
Would it make any difference if you took him with you to your doctor's appointment and had the specialist explain to him how much pain sex causes you? I kind of doubt it, because, from your description, it does sound like there is a lot going on there...issues of control as well as whatever personality disorders he might have, etc.
I personally have never had experience with a man who wouldn't back off when it became clear that my "no" was not a teasing one, but a serious "no". Perhaps there was then some discussion as to why...but, that was the end of it. This was before I was married, and long before I had back problems. My husband managed to understand that I just didn't even want to be touched as I was going through my various surgeries. So from my perspective, what you are experiencing is anything but "normal," whatever that is.
There has to be respect between a couple for a relationship to work, on any level. He just sounds like he never moved past the narcissistic phase of development...and cannot think beyond his wants and needs.
I'm really sorry you have to put up with all this, and hope you will be able to make some changes soon.