Yes, you should be concerned as the
lump is growing, and your ankle is swollen and painful. In all probability, this is an abscess or collection of pus. A lump at the ankle can be due to a cyst, a hematoma, localized collection of fluid, a varicose vein causing venous pooling, arthritis or due to infection. First consult an orthopedic specialist and get an X-ray and or CT scan of the ankle. This will give a clear picture regarding the swelling.
Take care!