I agree with Leesa, and I agree with your doctor (looking for another cause & treatment for ED). There are many possible causes; please read:
http://en.wikipedia.org/wiki/Erectile_dysfunction
and google other sources of information.

One cause that is not specifically addressed is the anxiety and stress that can accompany accute and chronic pain syndromes (like lower back pain and sciatica). Just something to consider/think about.

It may be a cultural thing (I don't know) but ED isn't as big a deal here as it was many years ago (in fact it's not a big deal at all anymore, and it shouldn't be), no doubt in part to heavy marketing of the three medications (Viagra, Levitra, Cialis) now available for treating ED. Typically, men go to their doctors, mention the problem, are screened for contra-indications (medical history & exam) and given a sample and prescription.

Medications are not the only options; that's a choice/decision between you and your doctor. Other options are explained in the link above and on other medical sites.

Doc