How do you even play as a Mage?

After two playthroughs of warrior builds I decided to do a mage build. I started with Breton because of their resistance, and also because I don't like High Elves.

The beginning was wonderful, I could blast fire and sparks while healing with the other hand. This worked till Whiterun. Now I have to fight a dragon, and it's one shot killing me every damn time. The mage robes don't provide any armour, without them my magicka doesn't regenerate quick enough. I have an alteration spell for boosting armor, oakflesh but it doesn't seem to do anything to the Dragons attacks.

I have only enough levels to get novice spells at half magicka for each school except illusion. How do you get good at this? Am I missing something?