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If you have looked at the main causes of menstrual cup discomfort (wrong size, inserted wrong, too firm etc), then you can chalk this type of unresolvable discomfort up to the menstrual cup brand being the wrong one for you. If this is the case, then you will have to select another menstrual cup model to get the best experience from it.
But do consider what you think it was about the menstrual cup that caused it to be uncomfortable such as the softness/firmness, diameter, length, texture, stem, bell shape and design- in order to select the features in another menstrual cup that may be more comfortable for you.