What Causes Lump On Labia During Menstruation?

I recently saw my OBGYN because of a lump on my labios. It was determined this lump was just a gland that was draining. It has been about one month since I saw the Dr. and the gland has completely drained. I started having pain, itchiness and discoloration in my inner labios however. I've had this before recently but it always seemed to occur during menstruation. This time, it has been about one week since my cycle. Any ideas what this could be?