Okay. I've been playing Dark Souls for three weeks now, and it's been a blast - the game is punishing, but rewarding, offers no hand holding, etc. It features an immersive online system, blah blah blah. 
 
But you guys already know all that. The thing is, I feel a bit lost and underpowered.
 
Don't get me wrong, I do know where to go and which bosses to beat. I am currently trying to beat Seath, have ventured pretty far into the catacombs and have beaten the lava centipede. I'm also considering beating Sif in the near future.
 
The thing is, I feel like I'm underpowered for my level, and can't figure out what to equip/buy/level up to deal decent damage. I have lvl 83, and am focusing on magic and dexterity - I have 37 and 38 points in dexterity and intelligence, respectively. I'm using a +3 lighting Uchigatana, a +5 enchanted Uchigatana, and occasionally the lifehunt scythe and the furysword. I've lately switched from the gold-hemmed armor to the Ornstein set, sacrificing my fast roll in the process. I use 3 spells: souls spear, homing soul arrows and the strong magic shield.
 
I just feel like I'm not doing enough damage. All the dex scaling weapons feel like they barely tickle the opponent. From what I've experienced so far, dex scaling weapons are a joke in this game. The enchated Uchi feels alright-ish, but considering that I won't be able to upgrade it more I feel a little disappointed. 
 
I guess my general question is: what am I doing wrong? I know that the game gives me a hard time, since I've heard of people who have beaten the game on ~40 lvl (I am also 60 hours into the game). Am I missing some incredibly powerful spell? Should I find a better catalyst? And in what way can I use my high dexterity, since it's been pretty much useless so far?
 
Thanks a lot for all the advice.