Nicole, what you are feeling is not unusual.
I can say that, as a veteran of 100's of classes, there are peaks and valleys, plateaus, extreme heights and occasional lows. Your body will go through constant changes, constant modification. Come to think of it, your mind and spirit will as well!
If what you got is all there is, that would be pretty sad, right? Now, there are plenty of times in your yoga future where you may feel you've gone as far as you can go, or the poses just don't get better. When those events occur, and I am sure they will, that is the time to re-focus on basics, from the soles of your feet up, from the tips of your upraised fingers down, and to become conscious of muscle movement and flexion, and of skeletal alignment, locating stresses and imbalances that restrict your advancement.
By doing these, by focusing on the small elements of the postures, your breathing, your focus, the symmetry of the poses and your mental aspect (and spiritual aspect), you may discover an endless path of expanding awareness, ability and knowledge.
omg, did I just write all that?
Anyhow, I hope this helps give another viewpoint to what you are experiencing.