Your spec is off, that's likely part of the problem. Touched by the Light is a crucial threat talent, because your Seals, Judgements, and Consecrate damage all scale with SP in addition to AP. You're also using some sub-optimal glyphs.
Try this setup: http://www.wowhead.com/talent#sZV0tAbuMusIufdxfMzbcGN
(You can take the points from Divine Sac/Guardian and go 3/5 Reckoning if you want, although it's a very small threat boost)
You should also go through your gems and get rid of the ones that aren't at least part stamina. I wouldn't bother gemming strength really, changing your spec and just getting more experience with tanking will be enough to give you good AoE control.
Getting the Triumph dodge libram would help a lot with staying alive in 5-mans (dodge is not so great against raid bosses, but is very nice for add tanking). So just keep at it, get more practice and keep collecting those emblems.