What could be causing erectile dysfunction?

Treatment depends on the cause. Testosterone supplements may be used for cases due to hormonal deficiency. However, the cause is more usually lack of adequate penile blood supply as a result of damage to inner walls of blood vessels. This damage is more frequent in older men, and often associated with disease, in particular diabetes.
Treatments (with the exception of testosterone supplementation, where effective) work on a temporary basis: they enable an erection to be attained and maintained long enough for intercourse, but do not permanently improve the underlying condition. There are different treatments available

Oral Treatment
3 different tablets are currently available from the doctor and these work when there is sexual stimulation. Depending on the treatment, it will need to be taken 20 minutes to 1 hour before sex and the period of time over which it works can vary between 3 hours and up to 36 hours.
Alprostadil
This can be injected into the penis or inserted using a special applicator – usually just before sexual intercourse.
Alprostadil has also bcome available in some countries as a topical cream (under the brand name Befar), and preliminary studies have shown a clinical efficacy of up to 83%. It has an onset of action of 10-15 minutes and its effects can last over 4 hours.[citation needed]
Vacuum device
These work by placing the penis in a vacuum cylinder device. The device helps draw blood into the penis. A ring at the base of the penis help maintain the erection. This type of device is sometimes referred to as penis pump and may be used just prior to sexual intercourse.
Hormone treatment
It is rare, but some men receive hormones for their erection problem. This does depend on the cause of the problem as well as other factors.
Surgery
Often, as a last resort if other treatments have failed, the most common procedure is prosthetic implants which involves the insertion of artificial rods into the penis.[26]
Counselling
Counselling is often a consideration, both where a psychological cause is suspected or must be ruled out, or to assist in management of any distress.
ED can in many cases be treated by drugs taken orally, injected, or as penile suppositories. These drugs increase the efficacy of NO, which dilates the blood vessels of corpora cavernosa. When oral drugs or suppositories fail, injections into the erectile tissue of the penile shaft are extremely effective but occasionally cause priapism. When pharmacological methods fail, a purpose-designed external vacuum pump can be used to attain erection, with a separate compression ring fitted to the penis to maintain it. These pumps should be distinguished from other “penis pumps” (supplied without compression rings) which, rather than being used for temporary treatment of impotence, are claimed to increase penis length if used frequently, or vibrate as an aid to masturbation.
More drastically, inflatable or rigid penile implants may be fitted surgically. Implants are irreversible and costly.
All these mechanical methods are based on simple principles of hydraulics and mechanics and are quite reliable, but have their disadvantages.
In a few cases there is a vascular problem which can be treated surgically.

In any case, good luck on getting your erections back.