I Was In A Car Accident 3 Weeks Ago And

I was in a car accident 3 weeks ago and I developed a soft lump on my leg by my knee that hasn't went down. It feels like tgere may be liquid inside and when I touch, pinch or scratch the surface I cannot feel anything. I can only feel when pressure is applied, it feels like the inside of my leg is burning really bad. What do I do? How long will it take to go away? Do I seek medical attention?