Hello, Thanks for your query. The large bruise is likely to be due to a hematoma formation in the area. Since the bony injuries have been ruled out, a soft tissue injury is likely. You need to avoid massaging the area and take a mild pain killer for relief. Avoid sitting for long hours. Do a cold compress on the area of injury. The pain and swelling might take over a week to subside. In case there is an acute pain and a sudden increase in swelling then consult your physician for a direct examination to rule out any infection in the area. I do hope that you have found something helpful and I will be glad to answer any further query. Take care