What Causes A Knot On Forearm After An Injury?

I'm a 45 yo wf a week ago I hit my (R) inner forearm, very hard, against the corner of a counter . It bruised badly with moderate swelling.. A knot, the size of a marbel ,soon appeared. At the time my pain was at a expected level therefore did not seek medical attention. The bruising/swelling are better, however the knot is the same and my painl level has increased to the point where I am unable to sleep. Is it possible something more serious than a nasty contusion has happened here? Thank you.
Jeana