Skin :: Mole Getting Bigger And Darker - Melanoma?

I am a girl, I have blonde hair, blue eyes, and my skin isn't pale but more "golden" colored. I generally tan pretty well in the sun and usually only get burned on my face and shoulders. I have never used a tanning bed before. however, I have a mole that's about a centimeter away from where my arm pit meets my chest that's concerning. It's much larger and darker than my other moles, it's a little bigger than a pencil eraser and is very dark brown and a teeny bit raised. The edges are chestnut colored and a little blurry, but it is still shaped like a circle (symmetrical). I am noticing it more often now than it the past, which makes me wonder if it has grown. I would get it looked at by a doctor, however the mole has always been covered by a swimsuit and to my knowledge, has never seen the sunlight. Does this mean that it couldn't be skin cancer?