If you pay for the internet then you can use it as much as you want!
Silly ungrateful kids
You say you are on a satellite link. Do you mean mobile broadband or do you have an actual dish? If you have a dish do you also then have an uplink modem attached to your phone line? As Robin has pointed out, cloud and rain can increase TCP NAK (Negative Acknowledge) errors over 3G broadband but for simple things like browsing the web and reading emails you wont be using up gigs worth of data.
A few things to try is to install a network monitor as suggested, also if you run wireless to share the internet connection make sure it using the highest security possible and change your passkeys etc. in case your network is being leeched. Make sure you have updated all your anti-virus software and run some scans to make sure your PC hasn't been compromised in anyway.