Can you link your armory? I'll run it through simcraft to see what you should be doing dps wise, a lot of people on here likely remember their heroic geared T14 toons with tier sets, sha gems, and good itemization so I feel it'd make it a lot easier if you linked armory.
Also you should definitely be using c bolt with procs that is the defining area of destro the ability to put out MASSIVE dmg in those few burst areas and can easily be a huge difference, even heroic geared warlocks will see their dps rise and fall nearly 100k just from bad procs.
I still think logs would allow the people here to best assist you, although now that I think of it, this post belongs in the 'fix my dps' thread chances are it'll be moved there soon so don't panic if you can't find it when you come back