sony a5000 picture issue

[cameraman 0]

So i have the sony a5000 shutting in shutter priority with the 16mm wide angle lens. For some reason it is constantly changing the picture from really light to dark. Now I know its going to change a bit but it going from and aputure or 8 to 13 and you can see it doing this really fast on the LCD screen just standing on the ground. Is there any thing i need to turn off in the setting that would be causing this huge issue. So I need some help with this issue if possible

[Zlew 0]

The iso button is easy to bump. I tape minde dowin on the 5100. Lost some pics by accidentally setting isolated to like 3200.

I shoot shutter priorit, auto isolated, aND shutter at 1/500 when shooting the 20mm for tandems.

[Finley1128 0]

What picture mode do you use? I'm using the sports mode and it doesn't give an option to change the ISO in that mode.

[Zlew 0]

Most of the time I shoot shutter priority (ap. priority if on a longer lens). I can check, but it's not uncommon for cameras to lock out some features on the more automatic modes like green box/P/sports.