Two steps forward, Three steps back

How common is it that a young singer, 24, would have a time where it seems like there is no vocal progress being made? Three months earlier I had been singing the best I ever had (according to my teachers). But then as the fall semester began again I just didn't make any progress, I actually picked up old habits I had been trying hard to rid myself of.

I just want to know if I'm alone in experiencing a set back like this. I want to have a more productive spring semester.

What did you do to help yourself move forward?
Thanks in advance for any insight.
-MZD