I had asked for some additional information and have not heard back.
The most common causes of pain in this situation are not serious, either a deep bruise
, also called a contusion, or some secondary inflammation. However, if it has been a couple days since the injury and there is an increasing amount of redness around the wound, there is a possibility that there could be an infection, either of the hematoma or of the soft tissue, called a cellulitis.
For the common causes of pain, it is appropriate to use ice for the first couple days and then use moist heat. An anti-inflammatory medicine, such as ibuprofen or naproxen, will usually work better than acetaminophen, and if there is a greater amount of inflammation, it may require a higher dose of the anti-inflammatory medicine. The ibuprofen can be used in doses up to 2400 mg per day, in divided doses, and the naproxen can be used in doses up to 1500 mg per day, in divided doses.
If there is an infection, though, it will need antibiotics, so it will be necessary to be seen by your doctor.
If I can provide any further information, please let me know.