as long as it doesn't hurt, there's nothing to worry about. The area's supposed to engorge with blood when aroused.
Actually, this sounds like a varicose vein to me. I just had an ultrasound today for this very reason. I found a similar smallish lump on the middle of the labia but it is always the same, no changes, and it can only be seen or felt when standing up, but I notice it. I went in to have some work done on my spider veins in my legs....for $150.00 a pop, they put a saline solution in the veins and the veins disapear. But, since I have not done this for over seven years they wanted me to come in for an evaluation. The doctor noticed some varicose veins in my legs and sent me to a specialist. When I told the specialist that my ob/gyn diagnosed that little lump as a varicose vein, he sent me for an ultrasound. One side is completely filled with winding, curving, thick varicose veins and the other side is normal. Very strange!
In my case, I am thinking that it is fall-out from my hysterectomy six years ago. This can be one of the side-effects. I will know more in a few days when I see my doctor. I have read that many women find out they have varicose veins in this area when they are pregnant. I did not have the problem then, so that is why I am blaming the hysterectomy.
Next time you are in for your physical/pap have the doc take a look. Again, when I lay down it is not visible. Makes for an interesting exam!
Mary