When you click on the Continue button at the top of your To-do list, you'll be taken to the last course step you looked at. When that's the last step of a week, clicking on the "next step" arrow will take you back to your To-do list, which can make you feel like you're stuck in a loop.
To get to the next week on the course, scroll to the top of your To-do list and click on the next week. For example, if you're currently on week 1, click on week 2.
Then scroll down past the Continue button and click on the first step of that week, and you'll be back on track.