Q: iPhone 6 loosing photos randomly

I have an Iphone 6 Running Ios 9.3.4

I have noticed that many of my photos randomly disappear over the last 12 months.

At first i thought it must be me doing something wrong however this last week i have been away with my son and took many photos of him doing various activities.

A few of these images i uploaded to Facebook (lucky)

We got home today and wanted to look at the pics to find that most of the pics were gone!

I have checked in icloud & recently deleted images but they are gone.

Why is this happening? I spend $1000's on a holiday with my young son for a week and have 8 pics to show for it.

To say i am unhappy...well i will leave it at that!