It could be because your cervix is off to one side. Perfectly normal. Or it could be that the Lily's built-in stem makes it too long for you and it only fits if it's tilted. I don't know if the Lily can be trimmed to be shorter or less pointy. Perhaps a more classically shaped cup would suit you better? Maybe one with a blunt base? Decide what you like and don't about the length, width, stiffness and shape of your Lily and use that to compare to other brands. Skim/Read https://kuradi8.livejournal.com/ for other considerations and helpful hints. The charts that it points to are out of date but there are MANY others online.

You probably have a tilted cervix, as I do. I had to sell my Lily as my tilt worsened (fibroid was pressing on the opposite side). You'll be happier with a blunt-based cup and a soft, cylindrical stem--I can't do flat tab stems at all for the same reason. If your cervix is low enough you may also enjoy stemless cups (there are a few models)