You almost never lose a game without making big mistakes. This is even true for very high-level players, although that's because they have a different idea of what is "big."
Moving the f-pawn early is generally considered a little risky. It can open up your King to various threats and doesn't help you develop anyhow. Of course 1.d4 f5 is a respectable opening but personally I'm not sure I'd recommend it at your level.
Notice how your early pawn moves made g6 and e5 into weak squares, which could no longer ever be defended by a pawn. This allows me to use my pieces freely; in this case my Knight, although I didn't accomplish all that much with this power. Be careful about this; it could have been worse for you.
4...h6 was also simply a waste of time in addition to creating a weak square and completely ruining the possibility of castling Kingside. I can only assume you were trying to forestall Ng5 because you've been hit with forks that way, but that threat is far away, and if I'd try it you can handle it without freaking out like this.
Your biggest problem though is that you never castled. Everything that happened in the last half of the game was because your King was out in the open. Once it was too late to castle, abandoning your King to go Pawn-hunting with 16...Qb4+ was also a mistake. Castling is absolutely essential in all but a rare few games and you should be planning for it from the start.