If you're not healing yourself you're probably using the default party frames intead of raid frames. Try switching to the raid frames (interface> raid profiles> check right hand corner and I like mine coloured by class). It's good to get used to them anyway, since you'll be using them for raids and pvp, and if you don't like them you can change them back, just give them a chance. The bars make health declines really easy to see, and your health bar will look like everyone elses so it's easy to heal yourself. Angellic bulwark is great for you since you're struggling to watch your health, so stick with it for now.
Seriously...gear makes a HUGE difference. I had the same experience at level 80, and almost quit myself. Everything you wear should be enchanted if possible and gemmed. All of your gear should have Int and Spirit on it (if no spirit on an item regorge haste to spirit). Your gear is completely off, and at level 70 that's going to hurt you a lot more than previous levels, and it'll only get worse from there.
Here is a quick easy reference for gear. It may not be perfect, but it'll help. Since you're quitting anyway, spend all your money to replace every item that does not have int and spirit on it, gem, enchant and reforge. Then try it and see how much better you feel. If it doesn't work out nothing lost.
My suggestion is to prioritise like this
Spirit (until comfortable...which will take a while)> Int > Mastery > Crit > Haste. Reforge all haste and crit to mastery.
My last guess is that you're not using mouseover macros or a healing addon, so you're clicking. That's extra steps to heal which will make you slow compared to how good you'd otherwise be. If you are forget this.
Maybe healing just isn't for you and you should try another class. It is hard and requires research to do well. Other class roles are more forgiving. Again, i'd like to re-assure you that healing is hard, and I was met with a similar crisis. I buckled up and researched stubbornly until I learned what I was doing wrong. Now I'm one of 3 main healers for our progressing MOP raid group, and I do very well. I love healing more than anything and have no interest in other classes (I'm a terrible tank though, and only so so at dps)
Whatever you decide, I wish you great luck on your travels. I hate seeing someone so down on themselves though, makes me sad *hugs*
Edited by Kirse on 9/30/2012 2:36 PM PDT