My iPhone 6+ is lagging like crazy?

I've had it for 6 months now and it's lagging a lot. Most my applications aren't working (they randomly freeze or turn off). The phone freezes a lot. The camera stopped working yesterday. Also yesterday (for like 6 hours) the settings 'app' would not open. It would either open up and just freeze or open up and it would be blank white, then it just randomly started working. Also sometimes when people try to call me it would either close before I could even answer, sometimes I'd answer and be able to hear them for a few seconds then it would close, or I wouldn't receive the call. And if that's happening I would try to call the person back but it wouldn't call. When I would try to use snapchat it would open up, I'd take the pictures then it just freezes. Instagram would open up, the pictures on my feed would start loading but then it also freezes. I tried rebooting, switching off my phone and resetting the settings a million times but it won't work. I also tried making more space by deleting things but that didn't help either
So if anyone knows what to do I'd appreciate that a lot because it's driving me mad

Do you routinely "kill" apps after using them? - double-click the home button and flick them off the screen.
Unless you do that, they are still loaded in RAM (and possibly running in the background).

It's something you should get into the habit of doing any time you close an app, with any apple device.

If you have not been doing that, kill everything that is open then restart the phone and see how it goes.

If you have done that with no effect, it's probably a corrupt update messing things up - mine had that problem a couple of weeks ago.

To fix that: Back it up a couple of times via itunes to ensure you do not lose anything.

Then, while connected to itunes, press and hold both the home and power buttons for around 30 seconds - it will go through different things on screen while doing that, eventually getting to a "Connect to itunes" display.

Do a full system restore on it - it's actually a reinstallation of the entire operating system.
That should be automatic when itunes "sees" the phone in that state.

Then, once it gets to the point of starting up as a new, blank phone, select the option to restore from an itunes backup & put your stuff back on it.

It's a bit tedious, but it works - mine is working brilliantly again & the battery life is excellent, after being in a state where things were going wrong all the time, it was getting hot and the battery lasted just a few hours.

Try a restore.

Make sure you aren't keeping a 100 apps open, close them out.