I have a pain while erection and also this remains ...

Priapism Persistent abnormal erection of the penis, usually without sexual desire, and accompanied by pain and tenderness. It is seen in diseases and injuries of the spinal cord, and may be caused by vesical calculus and certain injuries to the penis
This  can  cause  damage to  the penis , My  recommendation   is  to  seek  medical  attention , If   not  than  you  could  experience  more  issues  that  cause  permanent  damage  down  to  you

Doctor's say whenever you experience pain during erection you should seek medical attention. I know it may seeem embarrassing and you might not want to see a doctor but it's better to be safe than sorry. There may be a serious problem which will only get worse if you don't get to a doctor soon.