lack of strength in your case is due to the stimulus of pain that you have experienced during sex. Pain is the stimulus that is never welcomed and it ctreats fear and doubt in mind. This fear or doubt is the sole factor here that is not imparting proper pleasure, while sex is a pleasure game. If you really enjoy the act then only you will get proper erection. When a person is unable to fulfill his desires in practical way he dreams of sex and reaches end point causing nocturnal emission
. If you forget all about sex and never preplan then you will enjoy. The basic is you will have to kick out fears of your mind. There are number of herbs to cure your problem. To rule out the causes of pain during act , look for your fore skin does it retact easily or you have small opening that gets stretched and cause pain.