Since I was 15 I have always had "initial anxiety". It has always been a problem, and not a physiological one - when you are 15 and healthy you get a hard on when the wind blows.
It is not the same as "performance anxiety". I do OK in my opinion and a few others as far as performance. 
It only happens the first time with a "strange" female. Like an "off" switch is flipped. No matter how much I wanted to, it just didn't work. After I spent enough time with the woman and started getting more comfortable it would eventually happen. After the first time I would be unstoppable.
New female in the picture, same thing all over again.
It is "normal" for me. People are different, and I think the whole pyschology industry is full of crap if they label everyone who differs from the general population as having a "problem".
But it did "cause problems" for me(not the same IMO as "having a problem").
I did not try Viagra for years because I thought it would do nothing since I knew it was not a physiological thing. But a few years ago, I decided "why not?" Works like a champ.
I guess it provides enough physiological enhancement to counterbalance the psych factor and push me over the wall. If I take Viagra it provides enough boost to at least get enough of an erection to get started. After that I'm fine.
If you have not tried Viagra because you don't think it will work for you (i.e. not physiological) try it anyway. It may do the trick.
May take a higher dose since the strategy would probably be the same sort for you - counteracting a mental perspective by increasing the physical response. I take 100mg, the first time, then usually don't take it again at all with the same partner, or maybe occasionally 35 mg or so once in a while because I like the little extra kick.
Also as far as ADD goes - does this problem affect other areas of your life, or is it just sexual? I'm no doctor, but if it is not a (major) problem at work etc (and keep in mind everyone has bad days where they can't focus, that's normal) then I doubt seriously you have ADD.
SSRIs (Zoloft, Prozac, etc) are WAY overused in this country. The industries that promote them have basically created all kinds of "conditions" as a reason to prescribe them. ADD, "Social Anxiety Disorder", etc. While I believe that a small minority of people suffer from genuine chemical imbalances that drugs may help, I truly believe the majority suffer mainly from the pressures and anxieties that *we* put on *ourselves* in our modern lifestyles.
Too many people have lost sight of the fact that *true* quality of life does not come from money, keeping up with the joneses, constantly talking on a cell phone etc. Slow down a little. Life is about self-esteem, peace of mind, inner stuff. True fulfillment comes from within, how we treat other people, etc. None of which appears on your monthly paycheck.
There are way too many people on SSRIs today. They are not magic bullets, and they have adverse affects on sexual performance too.
Try things like maybe decreasing your caffeine intake if you drink a lot, cut back on smoking if you smoke, etc. Take a long walk everyday to just let your mind wander without control. Try a martial art, or yoga/meditation. These are all much healthier ways to reduce stress and develop mental control and focus than taking a pill. Hypnotherapy also seems to be really effective for at least some people.
The only pill I recommend is Viagra if you have not tried it. It really might do the trick.
But if you do feel like you need medication, try Bupropion first. It can definitely make you feel sharper mentally, but may be a little speedy at first. So it may make things worse, not better. But it is worth trying at least. It's not an SSRI, and unlike Zoloft, it does not have adverse sexual affects. Plus you don't have to take it for weeks and weeks before you know if it will help you. It is not as mentally dulling and probably does not tinker with your brain chemistry as much as SSRIs.
But overall I would suggest try finding a relaxing physical activity before you try anti-depressant/anti-ADD/Anti-SAD drugs, whatever they call them now.
Good Luck