data consumption

Ok, so yesterday, Friday April 12, I got an iPhone 5 with T-Mobile. From my knowledge I have a data plan that follows:

- 4.5GB of High speed data

- Then unlimited after I use up my High speed data

So it has been one day (and i dont think i'm a hige data user) and i've used 536.1 MB. This is alot because if I continue to go at this rate I'll have less than 9 days out of the month to use high speed data.

I did some research and it looks like that the average person uses only like 1 or two 2 GB in a month. How can i already have half a gig in less than a day? What is using up all my data? I've downloaded SOME SMALL apps. Watched a few youtube vids. And surfed the web.

So from what I know this "high speed" data means 4G. so when I use up my 4.5 GB What happens? To I go to 3G? EDGE? 2G? What happens? And if I do get away from 4g, what happens to my voice and text? if im not on 4g does my voice and text 'quality' lessen? Is there any way I can check why im using up so much data?

Thanks!

Heres some things I copied ans pated from my-t-mobile.com:

Services:

500 Value Add a Line

4.5GB Data SMHS Value

Data: 536.1 MB / Unlimited on our network (up to 4.5 GB high-speed data)