Frost DK, Low Health, High Defense Whats wrong?

[Shieldless]

I dinged 80 a couple of days ago and have never had a problem tanking, but with heroics rolling around, I found a major problem. My defense was up to 553 with Stoneskin Gargoyle, but my health was only 21K with frost presence. Ive looked around at other tanks with my gear level, and they all seem to be just fine. Whats wrong?

The World of Warcraft Armory (http://www.wowarmory.com/character-sheet.xml?r=Arygos&n=Hemmorrage)

My armory link so to see my current gear.

[Dargath]

Much of your gear lacks sockets and stamina enchants, that's all. Upgrade your gear and your health will pick up pretty quickly.

I had the same problem. Made tanking AN a bitch.