I have a small, round, blue, slightly raised lump in the middle of my left bicep. It's been there for years, I don't remember how many years, but around ten, I guess? It looks like a varicose vein poking up through the skin. It's been slightly sore the past couple of days, when I move my arm or press it, but it's not really that painful. It doesn't look like something in or on the skin, but rather just underneath it, like a vein. Any idea what it might be?