Coming from an iphone to android, i think you will always notice such a huge difference. I done exactly the same.
Dare i say it but ios is a lot more power friendly as it only has to work on 3 different phones whereas android has to be a lot broader in its approach.
There are multiple different things you can do to conserve power like make sure your brightness is as low as possible. Switch the screen off manually when not using it instead of waiting for it to sleep.
Facebook is a notorious battery drainer, it might be worthwhile deleting the app and creating a shortcut on your home screen to the website if you use it a lot.
All in all though, what you are experiencing is perfectly normal. You'll get used to it eventually though! On the plus side though, you can swap out you S4 battery, couldnt do that with an iphone!