Although possible, it is atypical for a vasectomy to lead to sexual dysfunction. You can consider further testing to evaluate the genitourinary vasculature (i.e. an ultrasound).
Blood tests looking at the testosterone, thyroid and diabetes can also be considered.
If either of these scenarios are present, ED medications will not be of benefit. Treating the appropriate cause behind the symptoms would be the appropriate course of action.
You can also consider another urological opinion if the tests and treatements are not improving the condition.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
http://www.straightfromthedoc.com