No matter I'm correct or not, remove 3 points in unholy and added in to blood death rune mastery, at least it will help your rotation a lot if you don't know how to do a rotation yet, after you got 6 death runes, you can just easily push 3 OB and then FS, I believe you will do better DPS, try

IT PS OB BS BS dump (when rune dump just FS and activate all cooldowns)
OB-OB-IT-PS-OB............

when you always have 6 death runes up, I don't think you will have problem with rotation, just keep two disease on the target, and do whatever you can.

Correct me if something I said was wrong