Siben is right. Even without ever having used a shield, I almost never die. I always throw up Stoneskin/Shock Spikes before I begin which negates a ton of damage. Even in the cases where I'm being ganged up on 3 to 1, between Cure and Sacrifice, I can always keep myself in HP (even if I can only attack every 6 heals). If you expect you're going to end up in this situation on a leve where a mob calls for backup, hit them with an AOE DoT spell such as Frost. This + Shock Spikes will keep draining their HP while you work on defense. Use things like Radiance to hit for decent damage without any cast time. Then when you have significant HP from your heals, Nuke them.
The trick is, always have a second heal for when your first is on cooldown. You can keep hitting Cure/Sacrifice back to back until you're out of the danger zone and can work on offense again.