What can be this?

2 days ago I noticed this between my leg and it hurts a lot. I never had this and I do not know what it could be. Excuse the photo

Update: Thank you Tara. It was a bartholin cyst . The size was keeps increasing and was makin me hard to walk, sit, sleep n even urinate. It was really painful and on Friday the Bartholin Cyst drain by herself . I was used use compresses and the help a lot . Today 8/6/18 I went to the doctor and the give me antibiotics.