I'm sure I made some real blunders in this game, but I'm going to post it anyway so I can get some pointers on how I could've played better (except for the obvious blunders, which I can figure out when I'm not tired enough to make them in the first place).

I was running low on sleep when I played quite a bit of this game; can you tell? 

well, that's where you went wrong then! I found my chess game vastly improved when i stopped playing after coming home from a long night of drinking. Perhaps if drunken moves were taken into account my rating would have been higher long ago, but alas this is not the case.

As you say, other than the obvious (you should have taken his queen on move 18), you missed several oportunities to go after his f6 knight (or wreck his kingside) from moves 4 to 6.  Say move 5)Bg5 h6 6)Bg4 d6 7)e5 dxe 8)dxe g5.  If you had started on move 4), you could have supported your e5 pawn with f4 to avoid the queen swap.