Hello,
Thank you for your query at DoctorSpring.com
I have seen the image that you sent and from the picture it looks like a vaginal abscess, mostly an infection.
The other possibility is a vaginal cyst which can be confirmed only by physical examination.
The commonest causes of a vaginal abscess is a chlamydial infection.
Are you sexually active? If so, is your partner at risk for STDs? Also do you have any whitish discharge, or difficulty in urination.
Kindly get back to me with answers to the above questions and i will help you further.
Regards.

Hello,
Thank you for the follow up.
There are two possibilities for a vaginal abscess. The first and very common reason for an abscess is a blocked bartholin's gland, where all the secretions get clogged and form a lump typical to yours. On palpation, it can be confirmed. Sometimes it gets infected, and the bacteria can come even from the natural flora of the vagina, such as E. Coli.
The second possibility is an STI ( Caused most commonly by either chlamydia, or gonorrhoea ). Normally in a monogamous relationship ( you both have been together for 2 years now - it is not that common ). But in both cases, a simple course of antibiotic such as Doxycycline will be helpful.
I will advise you to get yourself examined by an Gynecologist, who can physically feel the lesion, and based on that suggest you further management.
Regards.