What Causes Pain In Foot And Black Line Of 1cm ?

Hello, a couple of weeks ago, I started feeling a pain near the ball of my foot. It felt like there may have been a sliver there, but I have no idea how I would have gotten one. My husband looked and saw a fine black line (about 1 cm long) in the place where it hurts so tried to get it out as though it were a sliver, but it was nothing but flesh. Now, a week after, my foot still hurts only doesn't really feel like a sliver anymore and the line has moved to a C shape and over a couple of cm's. Any ideas what this is?