Had a similar problem which the Dr put down to to a stress / anxiety related cause (another story), was given Viagra and told to drink 2 ltrs of water minimum each day
Now stress has gone and completely rampant again. Viagra keeps the old pecker up and can manage 3 pops in an hour now
Mrs doesn't know what has hit her and still got plenty left for the odd punt unless it is like today (wait for it sob story coming) and can't find anything available after cancellation and regular not avail.... grrrr.. So don't know your circumstances but of stress is a problem then maybe cause without even realsing?