Thanks for posting your query.
Without an opportunity to examine the swelling ,it is difficult to comment on it. But From description , this hard lump most probably formed due to haematoma
formation which might get fibrosed or calcified.
I suggest you to consult an orthopaedician nearby for a detailed examination of swelling. You may get the X-ray of the area affected under his/her guidance.
Meanwhile give hot fomatation over it, You can take Tablet Motrin
1 tablet with food as and when required (upto 4 tablets daily).
Wishing you good health.
Dr Saurabh Gupta.