I've had this on the back of my shoulder for a few years. I know it looks like a mole on the photo but it's actually a hard, black lump under the skin. Maybe the size of a pea but flatter. It occasionally itches. I've (obviously) tried squeezing etc but nothing happens. It's not accessible enough to try anything else!
I had a mole checked a few years back and mentioned this to the doctor who just said 'don't worry about that'. Helpful!