Thanks arran-yeah, all was well for a moment (with merging) then i discovered that there was still duplicate faces on top of each other! I did a little research after you posted the response and found out that i think i have what's called lamina faces (courtesy of 3dbuzz):

Lamina Faces are faces that share the same edges (and thus the same vertices) and they are quite difficult to spot without using Cleanup. You can think of Lamina Faces as unnecessary faces that sit right on top of each other. Objects with Lamina Faces will still render fine, but render time is likely to increase as the renderer will compute Lamina Faces twice. Any smooth operation will produce strange looking results and a SubD conversion will report a Nonmanifold error. Lamina faces usually occur when you merge vertices on faces that share the same space.

So i tried the cleanup like you said and checked lamina faces and everythings fine! There's still one or two faces left but i can deal with them!

I still don't know how i did this but if you were stuck like i was then use clean up-it's pretty good for lamina faces!

Cheers