A lump in a private area

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Hi
I am needing help/advice. I am a male and very worried about my partner. Yesterday i noticed a large swelling on the vaginal wall area, this is new and was not present 1 day earlier. The lump is approximately 3 cm across and fairly firm to the touch. She was unaware of it until i pointed it out, it is not causing her any pain or discomfort but it worries me. Can anyone provide help/advice?

Google, or get her to Google, Bartholins Cyst, and see if that rings a bell.
They're quite common I think.

Or do you mean right inside?

Hello and thank you for replying, i mean right inside yes, approximately 3 cms or so. Thank you