I was not suggesting that you install an Anti Virus software. I asked because that could be the source of the problem.
Back up your phone to iTunes or to iCloud, or to both. The Davita app is an Apple App Store app, so a backup will save all of your data, and can be used to restore your device once you have eliminated it as the source of the problem.
First, make sure you are running the most current version of iTunes on your Windows machine - open the iTunes app, click on iTunes at the top, and click on Check for Updates. Then back up your device.
Here's how to back up your device: How to back up your iPhone, iPad, and iPod touch - Apple Support
Probably should back it up to both.
If you have photos that you have not imported to your Photos app on your Windows computer, then import them first: IMPORTING PHOTOS - WINDOWS/MAC
Then erase your device: Settings>General>Reset>Erase all Content & Settings
Set up your device as a brand new device (not from the backup). Play around with it for a few hours with the sites you have been having the issues with and see if the problem goes away.
If the problem goes away, then erase the phone again, and this time set it up from either the iTunes or iCloud backup.
See if the problem returns. If it does, then your software is corrupted, and you are going to have to set up your device as a new device.
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