Thanks for your query.Based on the facts that you have posted it appears that you had Priapism
which has to be treated by aspiration of blood from corpora cavernosa. Now you have developed purple spot near base of the penis .This is collection of blood thathas spread along the sub facial plane .
It will get absorbed within a week or two,
You may take antibiotics and anti inflammatory medication like Diclofenac
twice daily to prevent infection.