The battery life doesn't look that bad if it is mostly screen on usage. If you have had your screen on for most of the 4+ hours, then that's why the battery is low. If most of that usage is screen off usage, then something is definitely up with Facebook. If you haven't, then I'd try deleting facebook and reinstalling. I wish apple would show screen-on time.
Verizon, in my area, doesn't have the densest network and was always hanging onto weak 1X and LTE signals which never helped my battery. LTE signals with high "noise" (aka RSRQ) would absolutely destroy my battery as well as cause very slow speeds. Perhaps the network changed somehow and if you are getting terrible RSRQ (no good way to measure this on an iPhone unfortunately), that could absolutely be the cause.
The screen was off for a good chunk of those 4 hours. I was in class or driving for most of it.