How Long Before Bruises Heal?

Hi.
I'm a 21 yr old female. Last Monday, July 16, I fell off my loft bed (college dorm) while trying to get down (I was still kind of sleepy) and ended up straddling the dresser that sits about halfway under it. It got me on the left side, under the butt and partially in the pelvic area. I definitely hit bone very hard. The bruise was black at first and has now faded to purple (which i expected). It's been getting much easier to sit down but every now and then I'll sit down and hit a certain spot that hurts just as bad as it did when I fell. Tonight I realized this spot is actually like a knot that has formed. Is that normal or should I get it checked out? When should I expect it to go away if it is normal?