There's a few things.
You're missing out on a lot of enchants, and that's adversely affecting your health. Your avoidance is a little low, but not unexpected for your gear level. Gem your gloves, enchant your legs, boots, bracers, and gloves. Work on your Hodir rep and get your shoulders enchanted, and your argent crusade rep for your helm enchant. You're missing out on a ton of health and some avoidance there.
If you're just stepping into 10 and 25 mans with that gear, yeah, you're going to get one-shot. Don't bite off more than you can chew, work on that rep in 5-mans and get some gear out of it, then work your way up.
Luck is what happens when preparation meets opportunity. -Seneca
Everyone marvels at a square egg, but only the chicken understands the PAIN.