Diagnosed with a hematoma on my leg after a taking a hit to it. x-rays negative for fracture. i still have swelling on and off. i have developed a burning pain in the area of the hematoma that comes and goes later in the day. why is this? concerned?

The hematoma stretches tissue fibers which can cause pain. A direct hit to bone can also disrupt the sensory nerve endings at the bones' surface similar to the effect of a break. I find the cited effects expected for the injury described. It should gradually improve. Localized heat application can improve blood flow & speed recovery but could increase pain.