Hi, I am 29 year old suffering from erectile dysfunction in the form of weak erections. I can consistently get erections but they are not very hard and I am at the point where I can't have sex with a condom on (kills what erection I can develop).  The first time this happened was about six months ago, since then the problem has gradually gotten worse to the point that now my erections are always weak, including during masturbation and morning erections.  

Other than this, I am very healthy:  I work out around 4 time a week, I'm trim, I'm a long-time vegetarian and already eat many of the foods considered good for sexual health (fruits, vegetables, grains, fish oils, vitamin c, etc). The only negative health factor I can think of is that I have been a moderate smoker for ten years, although I quit recently when the problem became impossible to ignore. 

I recently went to a doctor and he prescribed levitra. This worked fine but the problem returns as soon as I stop taking the drug.  He also checked my hormones etc and said that all my labs are normal, meaning no thyroid or other hormone problems, no diabetes, very low cholesterol, etc. 

So obviously my question is what else could be causing my ED?  Could there be some type of bad carcinogenic substance in my surroundings, or is that just paranoid?  I think this problem is physical, not psychological but how can I be sure (do the morning erections prove that)?  

Will I need drugs to treat this forever, and will my condition continue to worsen? I am very worried and think I am now developing depression and psychological problems that may accacerbate my problem. 

Thanks.