gravitas said:
The attitude and knowledge around ED has changed a LOT in the last 10 years. Get yourself a GP (not just a medicenter quack) and have a proper discussion on why you think you may be having performance problems. Is it an issue with a specific partners or everyone. Do you have other health problems like high blood pressure, diabetes, etc.
There's honestly no better advocate for your health then having a GP. They are a great resource to help you with day to day medical concerns like your ED and god forbid you encounter something more serious you're in a better position to get access to specialists and enhanced tests if you have a doc who knows your medical history.
Good answer gravitas!
chubbyguy, there are a LOT of reasons why you could be having this problem, including anti-depressant meds, and the doctor you saw was IGNORANT, and in fact, potentially very harmful to you! As gravitas pointed out, some serious health problems need to be checked into and ruled out first and foremost.
You can have diabetes or high blood pressure and not even know it. My mother was getting her blood pressure taken by the cuff at Shopper's for months and had no idea what the astronomical number meant until she told her doctor what it was and saw the shocked look on her face! A reading with the cuff in the exam room confirmed it.
I have a client with diabetes who can get it up and keep it up for what seems like ages and I can have a good, long, glorious ride on him and he can only lay there and watch me and enjoy me enjoying him and take my word for how hard he is—he can't feel a thing.

God, how I wish he could genuninely enjoy it as much as I do, but the diabetes has caused nerve damage—what a cruel disease!
Get yourself to a qualified, competent physician ASAP! The longer you wait, the more risk of permanent damage being done if there is something serious causing this.