Hey there, since i cant find any recent logs i cant tell if you are doing anything wrong but i can give you some general tips.
After looking at your armory i noticed your gear is actually well optimized for your ilvl. Amount of mastery and spirit is really good, you should get set items as soon as you can they will provide decent boost to healing,get Demonic Phylactery and pair it up with Flickering Felspark and get legendary ring as soon as you can.
From what you said here i imagine you are going oom cuz you are trying to spam only chain heal which is wrong. You have to spread your riptides around raid by using it on CD to provide maximum amount of chain heal bounces with high tide, also cast Elemental Blast on CD, amound of spirit you are missing if you are not using it is huge. Healing stream totem should be using almost on cd as well ( its ok to delay it if there is not much going on at that point but generally you want to use it as much as you can ).
Hope this will help you for now, but if you could provide Warcraft Logs in future i can tell you exactly what you are doing wrong and what you should be working on to improve yourself as healer.
Edit: i just noticed you are using glyph of Water Shield, you should remove that as soon as you can its not good at all. Instead get Glyph of Spiritwalker`s Focus and use it when you have to move to reduce downtime on your healing.