Hi and welcome to HCM
From description , this lump most probably formed due to haematoma
formation (collection of blood) after fall which might get fibrosed or calcified.
It will take few weeks to months, sometime year to get disappear.
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).
I do hope that you have found something helpful and informative and I will be glad to answer any further query.