I have a large lump that has come up next to an old scar. I had a very large bruise first that lasted for about a week and a half. The lump is about the size of a large lime. Whatshould I do?

Could . Could be a keloid scar or a cyst or a hematoma(a collection of blood). You need to have it evaluated by a doc.
Any . Any large mass warrants a medical evaluation. It could merely be scar tissue, a collection of blood under the skin, lipoma (collection of fat) or a tumor (benign or cancerous). You will need to see your primary care provider first for an evaluation and possibly imaging studies, or a direct referral to a surgeon. Best of luck.
I . I am not sure if i fully understand your situation. If i understand correctly, the scar is from an old procedure that had healed long ago, and then you had a bruise form? Did you have an injury or accident that caused the bruise? Where is it located? What was the old scar from? Without an examination by your doctor, and further medical information, it is hard to know what you may be experiencing. There are many possibilities. You should see your doctor for an examination.