Okay.. So I'm a level 85 blood death knight and I tank. I was in a dungeon and the people in there kept on saying i sucked which is kinda a downer because I want to tank on a death knight and I don't know what I'm doing wrong.. Their explanation was that I lost health too fast which I don't understand why I would be. I'm just doing heroics at the moment. The link below is my character. Can you tell me if theres anything wrong with my character? And what i should do to improve it? My glyphs are Prime: Death and Decay, Death Strike, and Heart Strike, Major: Blood Boil, Death Strike, and Vampiric Blood, Minor: Blood Tap, Horn of the Winter, Resilient Grip.
Can someone tell me how I should do my rotations? I feel like I have the rotations right but I guess not. People were saying that I should be able to hold my hp high as a Death Knight but I don't understand. Any tips will help. Thanks.

http://us.battle.net/wow/en/character/frostwolf/m%C3%ACn%C3%ACh%C3%B9lk/simple