My Rengar dmg isn't there.

The past 4 games I've played Rengar I can't help but feel I'm doing no dmg to people. I do the nuke combo that I know how to do and it only half healths their adc. My empowered Qs even alone are doing nothing. I feel none of the empowered abilities are doing their dmg and the ult most of all isn't giving me any dmg output... I've mastered Rengar and usually do really well. I don't get what the problem is. Does anyone have a possible idea of what this could be? I mean, I love Rengar, but this current issue makes me want to drop him completely.