Q: iPhone Home Button, Storage, Messaging, and Other Problems

I started having problems with my phone a few days ago, and I believe the problems may have begun due to a a lack of storage.  I've gotten "storage full" notifications for months but haven't done anything about it.  (Dumb I know, but) I never deleted any messages and had on the setting for it not to delete any.  It said there were 6 GB of messages (on a 16 GB phone).  When it stopped working correctly, it cleared all of my message threads.  When I looked in settings however, it still showed the messaging app as using 6 GB of storage.  why and how can I remedy this?  At this time, messages are still coming through but it does not give me any notification (even after making sure notifications are on in settings) and my old messages are still gone.  As this is happening, the home button started acting weird.  It works, BUT only if I double click it. A single click will not bring me to the home screen, I can only open the multi tasking screen. I tried remedying it by using assistive touch but the single click still does not do anything.  I also cannot open the notification center or control panel at all. Any ideas on how to fix this???  I'm not sure what OS I'm on but I haven't updated in several months.