I had a septoplasty with turbinate reduction a little over a year ago. Is my nose collapsing?

Hard to say if the outside of your nose collapsed without a pic but it is possible to happen from a septoplasty. Your breathing issues may be due to a number of problems including nasal valve collapse, the septum deviating again, and regrowth of your turbinates.  I have done a lot of septoplasties in my 25 year career and am always careful to maintain enough septum in the crucial areas so that the bridge doesn't collapse but at the same time be aggressive enough to make sure that the deviation is permanently corrected.  In addition I believe in actually removing a small piece of the inferior turbinate rather than just shrinking them as the shrinking method sometimes doesn't last. Also if you had sinus problems to begin with a cat scan should have been ordered preop and if you indeed had sinus issues that didn't resolve with medications and/or allergy treatments sinus surgery maybe should have been done too. A septoplasty and turbinate surgery alone will not fix sinus problems 

Surgery on the structure of a nose has little bearing on how a nose functions medically. If you have allergies or chronic sinus infections, these conditions need to be treated as well as the structure of the nose for best results. Sometimes septoplasty and turbinate reduction can give you an opportunity to better treat the inside of the nose to improve infections and allergies.

Hello and Thanks for the Questions. 
It is difficult to fully assess your condition without a picture or better yet a thorough examination of your nose. That being said, sometimes septoplasty may not be adequate to fully optimize the nasal airway. Once the septum has been addressed it may unveil a collapsing nasal valve. If this is the case, it is something that can be addressed. However, my best advice is to see someone who is experience to addressing both the setpum and the nasal valve, such as an ENT trained Facial Platic Surgeon. 
Good Luck and I hope this Helps
Dr. David