SLA's druids dont get. This is probs its biggest downfall but I have covered that with avenging light from exalted angel and energy burst from draconic. I am also using rejuvinating cacoon which is affectivly a healing SLA so I am now in a position where I can go though quests without spending hardly any SP if I do not want to.
The druid is never going to be a sorc or even play like one. The druid has a good core of Great AoE spells, a Great CC spell and a Great DoT. I have basicly taken this core, specced heavily on positive healing so that my HoT's are as powerful as possible and then covered the shortfall of SLA's with epic destinies and twists.
What you are experiancing is completly normal at level 18. I was level 18 just last week and I felt the same. Burning sp to quick with no SLA's and only having 2200 sp... But it all changed once I got my ED's back.
P.S. I still use the DoT on trash lol. Most of the time I know if I cast it they are dead. And because there is vitually no cooldown or need for stacking, it works well.