Thanks for writing to us.
From description , this hard lump most probably formed due to haematoma
formation (collection of blood) which might get fibrosed or calcified.
It will take few weeks to months to get disappear.
I suggest you to consult an orthopaedician nearby for a detailed examination of swelling. Meanwhile give hot fomatation over it, You can take Tablet Motrin
1 tablet with food as and when required (upto 4 tablets daily).
Hope this helps you.
You can cosult me again directly through my profile http://www.healthcaremagic.com/doctors/dr-saurabh-gupta/64132