Thanks for the query,
It might be thrombophlebitis
It is an inflammation of veins.
Initially it might present as a painful swelling but later fibrosis
develops and it presents as a painless lump.
You dont need to do anything, just prevent injury.
If still there is bruise
you can use oint thrombophobe.
Please meet a dermatologist
for exact diagnosis.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.