Hi William,
I am almost 3 years post-op and still have great difficulty getting an erection without chemical assistance. I use 5mg. of Tadalafil ('Cialis') daily just for maintenance of blood flow to penis, but I rarely get any erection with this dosage. If you are using Sildenafil ('Viagra') then I would suspect that you need a full 100mg. dose. Even then, you will probably still need direct stimulation of the penis for any meaningful response, rather than waiting for a spontaneous erection.
I also use the 40mcg. dose of Caverject to get a useable erection. (The 20mcg. dose was insufficient for me). I am only prescribed enough for one injection per week, so I have to ration it :-). I have also sometimes had interruptions to supply, but currently there doesn't seem to be a problem. (I'm in Manchester and use Boots Pharmacy).
Best wishes,
JedSee.