You are having bruise.. A patch of purpura
There may be many cause..trauma,infection,blood disases, vascultitis, senile,connective tissue
In your case, it may be trauma..excessive scratching.
Take antihistaminics to relieve itching.
Take vitamin C
and K .
Apply thrombophob oint.
If it is relapsing, you may consult dermatologist
and go for investigations to have perfect diagnosis.
I hope you got my answer.
Dr. Ilyas Patel MD