Why is there pain?

Well one issue my husband and i have come across in the past few years is painful erections. This often leads to an inability for him to maintain the erection and continue with our sexual activity that day. I have asked many men why they think this happens. The most common response is trauma to the penis. Many men I have met say that they consider their circumcisions to be a large part of why they have painful erections. Most of these men are in their 30s or younger as is my husband. I asked my husband's urologist why men think this and he said it is a huge possibility that circumcision causes painful erections because there is less skin when the shaft lengthens causing stretching. Also he said that when circumcised, the head of the penis is no longer protected from "the elements" and can become hardened and less able to handle the continuous stretching and shrinking penises tend to do on a daily basis. I would love to hear from circumcised, intact, and restored men regarding this topic to find out their experiences.