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.

I'm with you on the dexterity front. I have 31 and am not putting anymore levels into it because the scaling does not seem worth it. As for the damage I just accepted that enemies take more hits now. It is not as crippling as it seems. I have gotten three of the major souls without too much trouble using +3 lighting spear and +2 Quelaag's fury.

i felt the same exactly and had same equipment.

get a scimitar. put it up to scimitar +10 which should be 20 minutes work. and then go to the black smith in anor londo change in to a demon weapon from the spider soul cant remember off top of my head lol and that is AWESOME once upgraded.

lighting spear pretty good fully upgraded.

i also found that the catacombs, tomb of giants and the hell place are just retarded and annoying anyway so u just have to grind through it mate

@imsh_pl: Truth is, you are really underpowered for your level. I think the average person beats the game between 60-80 on there first play through so if you're passing it before you beat Sif, there is a problem.

Physical scaling IS a joke! if you are using a lightning uchigatana and an enchanted one, you should not have increased dex past the minimum anyway. Get your lightning Uchigatana to +5 cus until they patch the game it will definitely be your best weapon.

having two stats approaching 40 doesn't sound good. How's your Vit and End look?

I've never made a magic build character so someone else will have to help you in the spell front.

What is your vitality and endurance at?  Often, I notice that people having trouble with areas is really just caused by a lack of HP.  Also the degree to which you split your main damage stat is probably hurting your dps.  The fact that neither of the weapons you use actually capitalize on the dex stat (lightning uchigatana doesn't at all while enchanted should only have a D in it) makes things worse.  Your best bet might be to take full advantage of the crystal ring shield crafted from the moonlight butterfly soul and a +10 shield.  It works particularly well on enemies with slow attacks like Seath as it does major damage but has a long casting animation.