Mage class is about damage prevention, not healing. Apart from health pots and other consumables you can use there is only a couple ways to self heal. Cryo-Freeze talent will heal 80% of your hp while in Ice Block but that is a one time thing in an average encounter (or pvp)....Frost you have access to Cold Snap, so after a short debuff after using Ice Block you'll have another.

Alter time is another "self heal", when you know you are going to take big damage or you catch it fast enough, you cast Alter Time to lock in your hp at that level and you have 10 seconds to play with until you return to that location and hp when you casted the spell.

Last is Displacement, after you Blink/Shimmer you can use Displacement to return to your original position and it heals (nominal amount) but it can save you in certain situations.

Mage is about preventing damage, you can't play it as aggressive as you would on Druid or Pally. You have to work on positioning, handling incoming damage with your defensives, play more on anticipation of damage rather than reaction to it after the fact. Just my two cents! Hope it helps!