I'm a first time user of the cup, so sorry about the length of this post!
First time I put it in, I forgot to rotate it. But it didn't have any problem going in when I used the punch down fold (in fact, it just sort of kept going to the point where I had to stick my whole finger in before I could reach the stem; it might have been because I masturbated briefly to relax my muscles). My period also hadn't "officially" started yet, but I wanted to put it in to prevent any spotting. When I took it out 10 hours later, I luckily didn't have any problems or leakage, and the cup was only filled a tiny bit (my first day is usually not very heavy).
Second time putting it in was more difficult. I tried holding onto the base to rotate it, but I had to let the cup go in a bit more under my pelvic bone, otherwise it got kind of painful letting it sit there while I tried to position it. Because I let it go in more, I couldn't rotate it. The stem was also only 1/2 an inch in, but sitting or lying down, I could feel it kind of protrude against my opening. I think my cervix lowered a bit since that morning, because the cup was sitting low. I tried removing it and inserting it a couple more times, but eventually my vagina became too sore, so I decided to call it a night and leave it as is. Overnight, it did leak, but the cup was only a little bit full. When I removed it, the only sound I heard was the "pop" right before it left my vagina; I'm not too sure what the sound of the "seal" breaking would make, or if that was it.
Third time putting it in, I tried again to pinch the base more and rotate it, but I still couldn't do it (not only is it hard to maneuver the cup so, but I can't find a comfortable position for my hand to do that). So instead, I just continued to push it in. I tried checking the sides to see if it was open, but even that was kind of hard (I couldn't quite get my finger between the cup and my vaginal wall). It's been about three hours now, and I've noticed some minor leaking. I don't feel it as much as I did last night, but walking around still gives me a weird feeling, like when you have a leaky tampon.
Is rotating the only way to get the cup to open fully? Are there other ways to do this? I thought one way could be if I pinched the base and tried wiggling it around as it moved up. The punch down fold works best for me, and I insert it with the folded tip pointing up. Also, will your vagina gradually get used having a cup be inserted into it and stop being sore? Mine isn't painful; I'm just a little tender down there, especially when I pee--it slightly burns. I haven't had sex in 2 years, so it's been a while since I've had to put anything bigger than my fingers up there.