DWing as Unholy is like masterbation. You do it alone, and no one wants to hear you talk about doing it.
If you have your heart set on playing unholy DW you need to be educated in one small aspect of the DK playstyle. All special attacks (aka any spell you have) bases it's damage on MAINHAND damage when its "weapon damage + xx extra damage". This means that when you DW (and this is true for any class that can DW not just DKs) you only attack with specials with your mainhand unless the spell specifically states otherwise (like mutilate for rogues). The reason why frost is able to be a viable spec for DW DKs is because of the 26 point talent in the frost tree called Threat of Thassarian. Read it and you'll understand why frost is the ONLY viable spec to DW as a DK.