Wide range of bizarre glitches on my iphone 6s plus?

So I have this problem with my Iphone 6s plus and I don't know what to do.

My iphone started glitching for no apparent reason, to the point where it's just unusable. First problem that I noticed was that I couldn't take pictures or videos, and the photos in my gallery don't load. (nor on my icloud when I tried to log on from the computer browser). Then I started having problems with other apps, I get error messages whenever I'm trying to open apps like spotify, whatsapp (new messages won't load) and others. Then I noticed that I was logged off from most of my social media accounts whenever I'm trying to log on from safari. Later it turned off and on by itself a couple of times. Many other functions are affected as well. I've turned it off then on a couple of times, and nothing is fixed. All this happened in a range of 4 hours. I have a perfect internet connection and the battery works very well, I have quite enough storage, the phone isn't that old either (i bought it 3 years ago), so I can't really think of a reason why all of these bizarre glitches are happening. I also wanna mention that everything worked wonderfully before, so I don't know why is this happening all of the sudden. If anyone here has any idea why and how can I fix this then please let me know. Thank u.