The swelling could be as a result of a collection of body fluid. It could also be caused by tissue growth or abnormal movement of tissue. Another possible cause could be an allergic reaction. It's advisable for you to see a doctor so as to get the right diagnosis.
Maybe injuries or even sores from an activity or exercise. see a doctor if this matter doesn't end in 4 days or if it gets worse after 2 days. Till then take a warm shower and keep your body protected where it hurts. This might mean you have to wear long clothing.