Nikon 18-35mm lens-edge of photo blurry?

I have a Nikon D40 and primarily I use the 18-35mm kit lens. I've had it for about a year and a half now and I've been having some problems with it. Well, first of all, sometimes it will be in auto mode but the if I touch the lens[the part where you would focus it if it's in manual] it'll twist and click. Once I take a picture, though, it goes back to normal but it's been doing that quite often lately. But that's not really a problem.

What I noticed today was that when I take a photo, the majority of it will be in focus but one edge/side will be blurry like there's a fingerprint on it. I cleaned the lens, both ends, and it seems to have made a little bit of a difference. But the areas of out of focus seem larger than they used to be. And it seems to have a harder time focusing.

I hate to think of having to replace the lens… Or God forbid, my camera. I think it's the lens though. I haven't tried my zoom lens to see if it's working better with that one. But I think since I've had problems with it it's the lens. I just wish it wasn't giving me grief lol. It's like 112.99 to replace it on Amazon and I just don't have the cash at the moment. Any ideas why it might be doing this/am I just paranoid?

Added (1). Ha you're right… I meant to put 18-55mm. Sorry for the confusion!

18-35mm Nikkor is meant for full-frame cameras. Are you talking of the 18-55mm kit lens?

Take your lens to the nearest authorized service center and let them check it up. Ask for an estimate if they suggest a repair. Plan according to the amount quoted.