I worked for a urologist for 7 years. You are perfectly normal to still take an interest in solving your ED. You should see a urologist, who can test you for diabetes, thyroid disease, vascular issues. Erections are an important barometer for men's health, so it's perfectly normal to talk about it. You want to find a urologist who specializes in ED, because even some urologists are more interested in this than others. Even doctors can be more shy or less shy about sex topics. So you could call a urology practice and ask for a doctor who is specializes in ED.
Alternatively you could just see your general practitioner and ask him to check you for common causes of ED, like diabetes, etc.
One supplement that can be helpful for vascular issues is L-arginine.