I have 2.5 GB monthly data. I've used 10% within a day.is that bad?

I just bought the iPhone 4 from Cricket on Saturday. I'm allowed 2.5 GB of monthly data. It's now Monday at 12:05am and I have used 10% of my monthly data? I've downloaded 3 apps and have about 25 pictures.

If I go over my monthly limit, my speed will just slow down(that's what a online sales-representative from cricket told me) So uh. I don't want that to happen ha what exactly is causing the data increase? Obviously the apps, but does pictures/text messages increase it as well?

You should try using Wi-Fi when you are at home for downloading large apps etc. To avoid using all of your data. Also, if you have an Android phone you can activate a limit in the settings to avoid going over 2.5GB. Images and texts are usually small sized files so you shouldn't have much of a problem with those.