Do you melee? At low levels I found my shaman went OOM constantly as well. I started turning on melee for single mobs while healing stream totems kept my health up. On multiple mobs I would drop Stone Claws to occupy them while I burned them down as quickly as possible till there was only 1 left and then I would melee.

You might want to pick up the mana reduction for totems talent as well, 5 points in resto I think.