Why is my Internet so slow/not working all of a sudden?

I had to go to my local library to even ask this question because it's too slow at home. My schools Internet went out yesterday, and now my Internet is suddenly complete ***. I've reset my router, disconnected the Wi-Fi, and even left the Wi-Fi alone for a while. Still nothing.

It was fine until like 8 AM this morning. My xbox won't connect to the internet 99% of the time and when it does, I lag like CRAZY. It won't even let me play single player games. My iPhone and iPad take about 50-60 tries to load a page, and pandora takes 30-45 minutes to load a song. It used to take about 1 second.

Why is this happening?

Added (1). By the way I'm only 14 so please don't give me a confusing answer I could seriously *** up my Internet permanently

Went over your qouta

You've probably just used up your limit for the month (or however long you get it for). For example, my family gets 60GB of internet usage a month, so we hardly have any problems, but when we used to have 10GB a month it was used up quite quickly so for the last week or so we could hardly do anything on the internet.
To find out if this really is the problem, all you need to do is go to your internet provider's website and log in. You should be able to find out from there whether you've used up all of your data.
If you find out that it is the problem, and you aren't getting it refilled for a while, you could simply buy some more.