Hi and welcome to HCM
From description it seems to be soft tissue injury
. Swelling might be due to haematoma
formation(collection of blood). 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 informative and I will be glad to answer any further query.