You actually have it backwards. Her sustain in the game is one of the best unless she's countered.
The ADC role is out of control right now, and a slight lead is deadly for bot lane. However Soraka has the ability to increase the sustain when her ADC is losing, and even cause her ADC to out trade the other that's doing better in farm and poke. This upsets the diva role because nobody is supposed to interrupt their road to late game, so she's frequently banned.
My typical order skill order early game is W>E>W>Q>W>R.
You want to max W as soon as possible for that cooldown. The Q poke for Soraka is super weak and easily avoidable. It also drains a lot of mana, so you don't want to waste too much time trying to Q poke. I usually use it if I'm bored, or if I know I can get 2 champs in there. Upgrade it last. Soraka is not a bully champion, and aggressive AP Sorakas don't even use Q that much early game.
E is the next ability you want to focus on after W. Use it anytime your ADC trades, dives, gets ganked, or you're being chased. It saves so many people. You want to max this ability second.
I usually take my HP regen. quints on her. I know a lot of people prefer AP quints, but maybe that can help with your sustain. I also take 6 mana regen. seals generally to help me better sustain.
When I saw the title, "Help Soraka help you." I thought this was about really scared ADCs being afraid to trade because that's usually the problem Sorakas have. They can't do anything other than save you and maximize your trading potential, so if your ADC is playing way too safely, roam.
My build goes something like this from game to game.
I start with
.
My core build usually ends up looking like this.

My other item is usually situational and based on what I need or my team needs.

I get
if I'm having fun or know my ADC. I don't normally die a lot as Soraka unless I am targeted a lot or have a silly ADC.
If I find myself being unnecessarily targeted, which happens a lot because some people despise Soraka players, I take
. I've gotten a quadra kill once as Soraka because people are so damn support thirsty in Gold or below. I've seen people throw team fights in ranked just to get at me. Soraka is strong, but she's not worth going 1v5 so you can kill a support.
My boots are between
and
.
Every Soraka has her own build, and that's fine. Diversity is a good thing. If you're really struggling with sustain though maybe some of my tips will help.