Suggest Remedy For Pain In Nerves On Penis

hi doctor,please help me,i'm is trouble.I usually masturbates,some days 4 times in a day.from last week i'm having pain on my nerve on penis specifically dorsal nerve,it comes and goes.erection is 100% ok,no tension with that.some days no pain,or discomfort,but if penis is erected for long tym then it starts shrinking like and pain on nerves.what i ahve to do doctor what is this,please help