You said you have tried doctors. Has he had a complete medical workup? There must be some reason for this, i.e. high blood pressure, or some kind of illness or problem. What did they tell your husband? Is he on treatment for it? Has he tried the "pump" that is advertised on TV? I've heard that it works very well. It might be worth a try.
If he hasn't had the complete workup, with blood work and the whole ball of wax, make sure he does -- or at least encourage him to do so not only for the sex reason but for his general health. If he has ED, something caused it, so it's a good idea to check everything out! God bless and take care! Hugs, Lee