Zong has one of the best 3G packages and offers highest downloading speeds.
"Some" apps that were downloaded were probably several 100MBs, as new phones constantly keep updating apps... in total you can end up downloading several GBs data just to update the phone softwares to latest versions.
Your mobile data should be off, go to google play settings and select the option where it updates apps on WIFI only (Not on 3G/mobile data)
Moreover search zong 3G packages, packages are competitively priced and economical and speed is good!