Well, the reason I was having pain was because I have an abrasion on my vaginal wall, and I got it from wearing the cup. I'm pretty angry about this, because I did everything right and I still had a problem. Basically, I was told that I could not wear the cup at night, and I could not keep it in for eight hours at a time. Oh, and I also can't use it for a few cycles until the spot heals. Which is extremely irritating to me, I'm in college, and the time when this cup would have been the most useful to me was when I was staying in hot dorms without air conditioning. But nope, not gonna happen this year. Also, I apparently may have a yeast infection from using it, which may be keeping that spot from healing properly.
Basically, I'm posting this as a warning. As much as people like to say cups are really super safe, they actually can cause problems. You really shouldn't wear it at night, and you really shouldn't keep it in all day without changing it. It's actually not safe. Even something normal like your menstrual blood can cause problems, because it isn't the same ph as your vagina. The change in ph can cause bacteria to grow there.
Basically, you should be treating it like a tampon. That's the safest way to use these products. Don't do what I did and assume the company wants what's best for your health, and what they say is accurate. It's not accurate, not by a long shot.
Now that the angry part is over, I told the gyne I saw about this site... it will be funny if she reads this post.