What Are The Signs And Symptoms Of STD?

I am sexually active, and I've never had any signs or symptoms of STDs (was tested clean about 5 months ago). My partner is clean as well. I have a line of skin on the underside of each of the labia majora that has always felt a little rough-- I just assumed that was part of my anatomy. I recently looked at my vulva in the mirror the other day, and one of those two lines looked very bumpy -- it didn't look like sores or anything like that; it looked almost like the skin had been chewed up, or like tiny, tiny goosebumps -- something like that. When I stretch the affected skin out, it looks more like ridges in the skin. I don't know if this is normal (I don't look at my vulva very often), although the odd-looking skin is in exactly the place where I tend to feel itch when I have general irritation (even when there's no yeast/bacterial infection). Currently, it doesn't itch, and it doesn't hurt, and I don't have any signs or symptoms of an STD. Any idea what this could be?