Partial impotence in otherwise healthy 30-something

My concern relates to some physical changes that occurred after an intense period of fairly rough sex.  My sex drive has always been extremely strong, and I've spent most of my life ejaculating at least once, sometimes two or three times a day, often through masturbation. I have never experienced any other form of ED and had a full physical including blood work about six months ago, from which I emerged in perfect health. But my problem persists -- a severe decrease in my ability to gain an erection and hold an erection, even though before I could become aroused just about whenever I wanted. Now I only gain an erection after some deliberate manipulation and even then it is rarely fully hard and I lose it once immediate stimulation ceases. I can (and do) still ejaculate but sex with a partner has become increasingly rare due to the difficulty I experience.

About a year and a half ago I was engaged in a series of sexual activities that were forceful but not seemingly dangerous or extravagant. Since that time, however, my penis in its flaccid state seems more flaccid than I have been accustomed most of my life and there is a noticeable lack of sensation (when flaccid) from about halfway up the shaft to the head. Often it feels colder to the touch than expected.  At times during semi-erection, there is a visible constriction (running across but more apparent on the right side) near that halfway point, as if some vein or other is not properly filling the shaft, but this constriction seems to go away the more erect I become, and is completely unnoticeable during erection and ejaculation. I have never experienced any pain in relation to this.

Also about that time, it seems that at least one deep blue vein on the right side became much more prominent in my flaccid state then it was before. I am wondering if all of this could be caused by some form of vein damage or blood clot and more importantly if there is an easy fix for my problem. I thought the situation would take care of itself over time but it has now been a long time and the situation stays the same. The lack of any pain has curbed my anxiety over the issue but the lack of sex, especially with regard to how I used to be, has grown unbearably frustrating. After the physical, my doctor downplayed the situation by offering me Viagra (which I did not take) and suggested that for a man of my health and age it was likely either psychological or something that would pass (as I believed it would), and as such I am shy about going back without any further developments, especially as the physical symptoms aren't readily apparent unless in the midst of sexual activity. I also still experience erections upon waking in the morning frequently enough that something clearly is still working correctly, if not for very long and if not at other times.

I've seen nothing else on the web that resembles my situation. Suggestions?