Leveling as prot = AoE grinding. You need a good shield, a lot of armor, a lot of stam and you have to use seal of wisdom/light a lot. You will always fight about 4 mobs at once but they won't hit you for a lot. If you can manage your seals/judgement well enough, you can fight forever and never run oom or die.
The AoE grinding will start mostly when you'll hit 40. Try to get the SM shield.
Talent up to lvl 47
Try this specc. Sanctuary will give you a lot of mana back. Reckoning is your best friend and will almost be up all the time since you will have a lot of mobs on you at once. Once you hit 40, get Holy shield for extra block and dmg.