What am I doing incorrectly?

Hey, guys.

I know that score isn't a 100% accurate depiction of how a person did in a game (I've been in games where the person w/ the lowest score was pivotal in winning)—but I think there's certainly something wrong when a person consistently scores lower than everyone else.

That, unfortunately, is my case. I've attached a replay that, I think, exemplifies my issue. Molecule (another player in the replay) is a very good friend of mine, who's been pretty gosu D) at SC since '98—and he consistently scores relatively high.

Is there something blatantly obvious I'm doing wrong? Something not blatantly obvious? Playing Zerg, was I macroing too much and not focusing enough on micro / harassment / etc.? I'm having a hard time focusing on a particular thing to improve. Any assistance would be greatly appreciated.

. . . More workers?