Ok so this game really wants me to just drop it like the obtuse piece of crap it really is.
I realised I had lots of unused soul items so spent a lot upgrading a shotel to plus 5 to get the quaelaags fury sword (had to buy titonite plus the upgrade fee) only to find out to go higher than plus 5 I need to go back to Andre. WTF! WHY?! Oh and guess where the game tells you that? No where.
That's some bs. Not sure I want to treck back to him so that's a bunch of souls wasted.
A homeward bone
halves any journey you make - it really does just take a couple of minutes to get to Andre then warp back again. But QFS isn't a magic salve, it's a decent weapon that scales off dex and humanity (as a chaos weapon), it has good DPS, but you could just put some charcoal resin on your current weapon and it needs Demon Titanite to upgrade it.
I feel your frustration, we've all been there - have some practice runs at O&S.
Don't expect to kill them, don't even hit them, just watch what they do, the patterns of their attacks, dodge them, try to separate them by using space and the pillars. Smough is way slower, so you can lure Ornstein away from him, get in a hit or two and lead him away again. Don't be greedy.
You might even want to go back to Firelink (because it's very quick and just a matter of running there), set up camp there and do the Catacombs - the boss of which is one of the easiest in the game and allows you to kindle bonfires to their maximum. 20 Estus Flasks can make a huge difference when you're having trouble with a boss because if nothing else it can help you last longer and get in more practice and see what the boss actually does rather than getting smashed in a few seconds of walking through the fog door.
These are just options, but you have more options open to you than just banging your head against the wall with O&S.
O&S is a HARD boss. Probably the most challenging in the game, it's two big enemies and a long fight. You don't suck because you're having trouble with it - it's designed to get you to push through the barrier :)