I Am On Avodart Capsules 500mcg Have Been For About

I am on avodart capsules 500mcg have been for about for years ,I was diagnosed with enlarged prostate but do not have any problems for at least last three years or so I do seem to have a problem with getting and maintaining an erection and have tried various tablets like viagra and lavitra and cialies but the all give me a head ace with not much result ,my question is is it necessary to be using these capsules permanently like I am told as I feel they are part of the problem that I experience I am nearly 68 and quite fit and active