How can sudden breathing problems after 6 months post op happen?

Hello! Thank you for your question. As far as I can understand from your question you might have stenosis inside your nose. It would be more convenient to decide with face-to-face consultation. Best Regards!

Questions that would help understand this better: Is your obstruction constant or intermittent? Is it one side or both? What gives you ANY relief of the problem? Spray decongestants? pulling on your nose or cheek?
See your nasal surgeon as that person is most intimately associated with your nose and what exactly was surgically done.
If that doctor doesn't give an explanation and possible solution (which you may or may not like/agree to), then consult with a surgeon who is experienced in revision rhinoplasty as this surgeon will likely have faced similar situations.

In the absence of nasal trauma, the only structure that could change inside your nose 6 months after surgery is the size of your turbinates. If you do an Afrin trial and breathe better, you could consider topical therapy like nasal saline and Flonase nasal spray, daily. Hope this helps! Dr Joseph