Thanks for the query,
Probably you are suffering from lipoma
Your description matches with it.
It is a benign collection of fat.
However usually there is no bruising.
Dont worry it is not a serious thing.
The only possible treatment is surgical removal,
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.