Generally you’re going to be analyzing the same lines of code (or the same projects) over and over again, so when you’re trying to keep an eye on LOC growth, how many LOC are scanned in a month isn’t really helpful.
What you can do is check the License page (Administration->Configuration->License Manager) for your current server-wide LOC count. That information is also included in the System info bundle (Administration->System->Download System Info) albeit in a less readable form.
If you’re worried about suddenly running out of capacity, you should be aware that your server will automatically send you a notification when you reach a certain threshold on your LOC allowance. I think the default is 80%(?) but it’s editable so you can set the threshold low, and re-set it at higher increments as your instance grows if you like.