So, this is a variation of the ol' "I'm a virgin and my cup won't fit" post.
I'm 28. I'm a virgin. I can use tampons without any real issues, and I can fit a finger up there without problems. I read the virgin's guide to cups that someone posted here. I bought a Moon Cup (the Keeper one, not the UK one) last month, started my period last night, and decided to try it out today.
I initially tried the labia fold from that one YouTube video that's often linked here (sorry, I can't find the URL at the moment!), because I was concerned about the bulky lower part of the cup that you get with the triangle fold. There was a burning and stinging sensation around the outside of my vagina, along with resistance right at the entrance, so I'm pretty sure it's my hymen that was unhappy with this. Tried a couple more times with the now slippery cup; still no luck. I switched to the triangle fold, with the same results. The cup is now washed and sitting on my bathroom counter, and I'm wearing pads again. And I'm a little sore down there.
Any other suggestions? I'm thinking of just returning the cup at this point.
Edit: I've tried again, standing in different positions and using different folds, and once I get to a section of the folded cup that's wider than a finger, it stings and there's resistance. I have no reason to stretch out my hymen beyond using a cup, and I don't want to use a cup badly enough to deal with pain, so I'll be returning it. Thank you to everyone for your help anyway!