What Causes Swelling And Bruising Of The Foot?

Hi about 2 weeks ago my left foot started to hurt. It felt like there was a bruise on the top of it. pretty dead center of the foot, about 3 inches down from the middle toe. I am a server so I am always on my feet and I notice I have a little limp when I walk. It throbs everytime i walk on it, and I just got done running on it, and it hurts 10x worse. (dumb mistake on my part) Like i said it feels bruised, but there is no discoloration at all! It's just a little swollen. I have no idea what I did to it at all!