Well your avoidance sits at about 38% which is a bit low but that will increase with a few better pieces of gear. You want to get the Conqueror's Darkruned Chestguard via Emblems of Conquest (run a couple heroics). The Sigil of Deflection is great via Emblems of Conquest as it will give you a good % of dodge, and has a good uptime (provided you have macro'd Rune Strike into all of your abilities, or at the very least, do use it every time it is up). If you are using Sigil of Awareness for threat, I guess stick with it for now but definitely pick up the Emblems of Conquest Sigil and try it...see how your threat is without Awareness. Your defense is fine at 543, so that is not the cause of your problems.
It could just be your healers, but before you look at that aspect, you want to see how you are managing your defensive cooldowns (Unbreakable Armor, Icebound Fortitude; you do not have a good on-use trinket for avoidance or mitigation [armor or dodge/parry/etc]). Your spec is alright but there are certain talents you don't need, such as Morbidity because you have probably the strongest AoE threat move: Howling Blast. You do not have 3/3 Improved Icy Touch which, unless you are relying on someone else for that (highly doubt it), you want to take it as reducing the enemy's attack speed is great. With 5/5 Bladed Armor and 3/3 Scent of Blood, you will not need your Sigil of Awareness for threat as you'll have enough RP for Frost Strikes (no Death Coils), and about a 650-750 attack power increase.
Try out this Frost spec (courtesy of EJ):