Same problem.
diabetes causes the viens to shrink so less blood flow to our important part..
i was a bit worried about mentioning it and left it months before having the courage to ask my diabetes nurse.
when i said ablut my problem she explained what happens because of diabetes and then told me to see the doc.
i get 4 viagra 100mg a month,which is the nhs limit.
I must say its perfect and works very well(or so i am told).
dont be worried as when i metioned it to nurse it was like asking whats the weather like!
very laid back and a very very common thing for us men,,
good luck