It sounds like you moved ahead to a new category (month) and want to get back to a previous category's lessons.
To do this, you should click "Categories" at the top of the lesson or category you are currently viewing.
From there, you'll be able to click the category you want to navigate back to, which contains all the lessons from that category. You can also skip ahead the same way to any lessons you currently have access to.
Here's a video in action of how to navigate your course:
But if that doesn't resolve your problem, you can submit a ticket right here in the Help Desk, and one of our representatives will get back to you as quickly as we are able!