When using Shiptheory, you will have a monthly allowance of shipments that you can use over the course of the month, the plan you're on will of course change how many shipments per month you have. You can check your month's usage, refresh date and current plan on the Billing History page which can be found in the "Advanced" section of your Shiptheory dropdown:

It's important to note that not all shipments that come into your Shiptheory account will count towards your month's usage. Only orders that are complete will count. 

This means that orders that haven't yet booked in and generated a label won't count, such as orders that are Ignored, Failed or any other status than "Completed". Please see here for some more information on Order Statuses in Shiptheory: Shiptheory Statuses Explained

If you believe that this is not the case in your account, or if you have any issues or questions here, please feel free to Contact Support.