How can I diagnose what is using my 3g connection in small packets
To diagnose the issue you could try a third-party network monitoring tool - Network Connections


  Powerful tool that displays and monitors (tracks) all inbound and
  outbound connection from and to your Android device.


Other features bundles in the app:


  
  Monitors all internet connections from and to your Android device
  Displays notification when hidden apps are connecting to remote servers
  Displays detailed IP information for each connection - IP address, reverse resolving (PTR), AS number, Abuse RBL data, administrative
  information, etc. 
  Gets detailed info about each app that connects to remote servers and network connections used by it - permissions granted to each
  captured package and all IP addresses used by it.