I've played about 50+ games as Soraka... her main strength is early laning, that and after she gets some ap (soulstealer, archangeals staff, zhonyas, exc.)
If you're losing lane constantly, there's probably a few things going wrong.
(1) your adc doesn't know how to play with new Soraka. In allot of matchups he should be getting in fights and harrassing/zoning a ton in the early lvls (especially lvl 1) since Soraka's heal is utterly broke OP then. Soraka kinda needs the adc to take advantage of her great healing in lane or else she tends to slowly become worse and worse than the other support.
(2) you should be running hp5 quints. There is never a reason not to. In allot of matchups you should start coin or 2*rej beads (20-25hp5 lvl 1) so you have utterly preposterous sustain. It lets you top off your adc fight after fight.
(3) Equinox is a VERY skill dependent skill, you need to be able to lay it down very quick and accurately in allot of situations. Like on a thresh right after he hooks or flays so he can't fallow up, or in front of the adc so he can't fallow up a supports harrass/engage, or far enough in front of the enemy that it triggers the root when they run through it, exc. It is a very tough skill, wiffing it or casting it for no reason can end up costing you guys your lives.
(4) You probably spam starcall. That's a big fat no no. The only way you OOM as Soraka is by using starcall way too much. In early laning you you should mainly rely on hp5 and pots for hp unless you're lane really needs more sustain so you level up the heal to rank 3~. Short of that it's mainly just a counter skill, like when the enemy tries to engage or poke when you can really use the extra dmg and chance at a snare. They will be closer and you can roughly guess where they will be going, so you should have a decent chance at a deadcenter shot. Unless you're stacking tear or just have above 70% mana.
(5) you probably aren't building the right items. As a rule of thumb, build as much AP as you can get away with. AP is as good on Soraka as it is on a mid champ. I tend to rush an archangeal's staff or soulstealer if we don't seriously need the extra disengage from frostfang/coin. Tear ends up giving infinite mana after a bit, archangels gives massive ap, it gives a better version of hp (a shield). 120 ap is like 72 more health a cast or 30~% more healing + much better sustain from starcall.
Ideal build order: coin -> tear -> sightstone -> archangels -> ionian treads -> zhonyas.
I only start rej beads when I know the adc is good or we seriously need to get ahead early on or we lose lane, coin makes stacking tear much quicker.
Anyways, my main issue with her is that she is a snowballer.
AP is so beneficial, she has such awkward/delayed disengage and is so bad at mitigating adc dmg that she is a snowballer.
Either you get ahead and her healing stays utterly obnoxious, or the enemy adc gets items and kills you're allies faster (making her W worse) and Soraka doesn't get gold for ap (making her W even worse) and with her not being reliable at disengaging from fights so she can heal up the adc (making W even worse)... the enemy can just shove you out of lane hard.
It makes her just an obnoxious toon all around.