I got a big dark bruise on leg with lighter colored lump in the middle. Hasn't improved in 4 days. No pain except when touching the lump. What to do?

"Normal bruising" It's likely that you bumped into something but didn't pay it any mind. The lump is probably a small area of bleeding( hematoma). This area will slowly resolve with the bluish color turning yellowish and then disappearing. No specific treatment is needed. This type of bruising is common in the lower extremities. If you have frequent development of bruises you should see your physician.