What Causes Recurring Itchy Lump In The Vagina?

Hi, for a while I ve had this reoccurring lump under my skin just on the inside of my bikini line. It would itch, and feel like a bug bite almost with a small lump, then be gone the next day. Now it s back, and has stayed back for a few weeks now, and has grown quite a bit. It s about the size of an oval shaped nickel, a bit red and sensitive to touch. There s no whitehead of any sort, just a moveable bump under irritated skin. I ve applied a hot rag with little pressure a few times, it seems to help a little temporarily, but nothing too dramatic. What could this be?