Hello Dr,I have had poor ability to sustain erection.this has occurred from my teen until I discovered the use of seldenefil which worked well for me during my 26-30 yrs of age helping me gain erection even over days. But right now in my 35 ,the seldenefil isn t working as it use to work for Me. Although I currently have hernia which am yet to undergo surgery.pls what could have lead to the poor efficacy of this drug which was once very useful to me.thsnks