Iphone 6 does not upload photos to I cloud.

My Iphone 6 tells me it's time to upload photos...which is something I already know. The settings are set to upload automatically. When it works, its great and I see my photos on both my phone and Ipad. I've taken my phone in twice to the Apple store. Their fixes work for 3 or 4 days, then the same issue comes back. I've updated...restarted. I am very frustrated with Apple. The syncing my phone and Ipad is one of Apple's best features. When it doesn't work, well, hello Google cloud.