Stop Facebook and Instagram from running in background
Applications like Facebook messenger, always leave a few processes and services running in the background. Even using task killers is not very effective in preventing them from running, because soon they will continue running.

In a situation like this, hibernating is more efficient because it takes care of both the proceses and services running in background. It will also prevent that application from starting up again until you start it.

Having said that a good remedy is to use hibernation applications like Greenify and see if it resolves the issue. The good news is that it is available for non root users as well.

More detailed instructions for setting up are found here: How to Optimize Your Android Phone’s Battery Life with Greenify