What Causes Swollen Lump In Vagina?

I have a swollen lump on the side of my vagina. I went to see a doc today and she said it is NOT bartholin cyst but a vagina infection. I recall having this problem before and another doctor said that it is bartholin gland inflammation. Clearly I am very confused as to what it really is It developed big overnight and is now causing me a lot of pain. I was prescribed antibiotics. I would like to know why I got it back in just 9 months?