Fast forward a few months later. I decided to give the medium Meluna a try. I inserted it, rotated it a little, felt it open all the way... so far so good... and then I realized I couldn't get it out. What I thought was a short vagina is actually a lot longer than I thought. The cup formed a very tight seal with my body and migrated way up beyond my reach unless I was bearing down and searching, and then I could only feel the ball part of the stem. I was pretty freaked out at that point, so I decided to give it a rest and wait until I was more calm and relaxed to try getting it out.
I finally ended up getting it out, with a combination of bearing down, searching and trying to break the seal by pressing on the side of the cup (I heard a funny sucking sound like air was getting in, so I figured that was the seal breaking), and then holding on for dear life when I finally got a grip on the ball stem.
Good aspects of this whole ordeal: I did have the presence of mind to realize that the cup had gone in and opened really easily, wasn't causing me any discomfort, and wasn't giving me trouble while trying to pee. Also, when it came out, I did notice that my blood had ended up in the cup. So it was definitely in the right place.
I'm pretty sore down there and a bit shaken up over the whole experience, so I think I'm going to stick with cloth pads for now before trying cups again. I'm still not sure if I have the right size cup. I like the Meluna, but is it normal for a cup to travel beyond your reach? Is this just part of the learning curve (I'm wondering how on earth I will ever get this cup out while I'm in a public restroom and can't kneel on the floor for ~10 minutes)? I really want cups to work for me. What do you all think, is this a fairly normal experience?