Everyone has a different libio - sounds like you have a low level of sexual interest - you describe yourself as asexual (although you do masturbate?). It is not that uncommon to have a low level of sexual interest - the image presented on television that everyone is having sex all the time is simply not true. You may just naturally have a low libio. If this is a major concern you can speak to a doctor about it.
Having a narow vagina can be caused by surgery or medical conditions - but it sounds like you have had a physical to rule these out. I had a partner who had a very small vagina and a thick hymen which caused a lot of pain when we first tried to have sex. Her doctor ruled out any medical conditions, performed a minor incision to remove the hymen, and then gave her excercises to allow her to slowly allow her vagina to stretch. It took about a year (which was embarrasing but fun!) but by the end we were able to have normal intercourse. You might speak to your doctor about this.
I think one has to do what makes one happy and conforming to others' views of how to express one's sexuality isn't necessarily the best option. You really don't have to have a sex life if you don't want one and I can think of few things less pleasant than unwanted sexual activity.
I went to the gynecolgist for the first time yesterday and she seemed amazed at the smallness of my vaginal opening. I got the impression that she had never seen one that small and was a bit at a loss as to what to do about examining me, because none of her equipment fitted, except one speculum that was designed for children. And even that was painful.
In my case I also have uterine fibroids (why I was there) and a good way of treating those is by inserting a device into the uterus that delivers progesterone there directly. Only we can't insert it without surgery. Normally it just goes right in because it's designed for a "normal" vagina.
So I'll probably have to have a small operation to open things up so we can put in the device. Apparently oestrogen creams, etc. won't help. The opening actually has to be surgically remodelled.
Like silverrose, I have to reply because this describes my problem perfectly! I've never been able to wear tampons (not even the teeny tiny ones my mom uses). Years ago I was given a Diva Cup, which I've never been able to use, it's even wider in circumference than a dry tampon, so that has always been right out. I've always wondered why I've had trouble. I used to wonder if it's vaginismus, but I don't think it is. Just now I tried to use my Diva Cup again, and to make sure I had everything positioned properly I stuck my finger up there as far as it would go. There was enough room for that, and that was it. I tried to see if there was some "wiggle room", there was none. It would not give. On one side (the "upper" side), there was something very hard, I'm not good with the anatomy, so I don't know if it was the pubic bone, but it sure felt like there was a bone underneath for how hard it was, so no give in that direction; and on the other, there was tissue that would not stretch or anything. I don't think it's vaginismus, for the same reason as OP.
I would love to know what I can do about this, for instance the kinds of exercises your doctor had you do, because if I don't do something about this, I won't ever even be able to have sex, let alone use my Diva Cup. The instructions say if you insert it properly you shouldn't even feel it. In my case, I would have to say that is complete BS, considering how I'm feeling in there right now just from having put my finger up there for a few seconds, and considering I can't even get the Diva Cup into the opening of my vagina, let alone *inside* my vagina.