What am I doing wrong?

Recently my pride took a huge blow, I let my 12 year old cousin fight in a few invasions using a CMG build (he fell in love with that spell after seeing someone killing me with it) I made a quick Katana build and let him host in the burg.

He dominated every fight he was involved in, his Kill to death ratio being closer to 3:1 while mine is probably round 1:3. 

Anyway, the point is that seeing him made me reconsider my current play style, which I try to keep varied (switching builds at the drop of a hat attempting to keep things fresh); but since I change how I play really often I haven't mastered any weapon, spell or tactic at all. Now I consider myself at least somewhat decent at Pvp; but I begun to wonder if I should stop doing that and focus myself.

The point is that I just don't know what to do, I love Dark Souls; but loosing that often is beginning to take it's toll on my enjoyment of the game.

I think that is definitely a fantastic idea if you wish to hone your PvP skills some more, I try to use a weapon for as long as it takes me to get good at it and have a positive win/loss ratio.  Even if you get bored of a particular weapon and want a bit more variety, while still retaining that general weapon class, just switch from say a Claymore to a Bastard Sword if you catch my drift.