This is definitely something that needs to be addressed - priapism lasting longer than 4 hrs can permanently damage the erectile tissues of the penis, to the point you could be permanently unable to achieve erections again, even w/ Viagra, Cialis,
Levitra, etc. There are certain medical conditions that can cause this - sickle cell anemia, for example. If I were you, I would not let this go - keep hounding Dr's for an answer. Have you seen a Urologist?