LG G3 Cat.6 — Why do Google apps don't work on my LG G3 Sprint?

I bought this phone from eBay, it was a great deal and is unlocked. The problems I'm facing is that I can't access Gmail, Contacts don't get synced, I receive no app notications, Play Store would stop working after two downloads and then won't even open up. YouTube doesn't work either. The software version running is LS990ZV4, and is 4.4.2 KitKat. I tried resetting the phone, clearing the cache of Google apps, uninstalling updates, but none of it worked. Chrome and Google search works perfectly fine.
Please help.