You can check your bandwidth usage as well as your upload usages via your profile page.
Then you can access your usages via the "Usage" tab.
From this page you can then access your usage over given months (by default the current month).
It will tell you how much you have used of your allowance. The bars themselves will change colour depending on how close you are to going over your limits.
If you go over your limits. You will be shown an estimated cost of the overages that you could charged. If you are consistently going over your limits, then you should consider upgrading to a higher package or adding more bandwidth/minutes to your account for an additional cost.