Hello! Thank you for the query. As Coumarin prolongs blood clotting, the most probable reason of your symptoms is hematoma. Due to recent injury some veins were ruptured and blood has appeared outside the vessels. Coumarin patients usually has such hematomas much larger than other persons. According to mentioned symptoms, most likely you need surgical intervention. The hematoma needs to be incised and drained. Otherwise the inflammation which is present will get worse. Hope this will help. Regards.