Sounds to me it could be an ingrown hair?
hey,
Because im not sure how big it is this answer may not help. I had a lump on my vagina about 3cm in diametre. It was round and felt hard and was very sore to touch. I went to the doctor about it and was told that the vagina has its own sweat glands and the lump was just a blocked one of these. He said it would go away in its own time. Surely enough it did!
Hope that helps!