Nasal breathing function is complex
Nasal breathing function is complex, because there are a variety of reasons for nasal obstruction, of which, nasal septal deviation is a very common one. A straight septum is required for efficient nasal breathing and the concern is that there is persistent deflected septum veering towards the 5% breathing nostril. I call it "finesse" surgery as the required component for achieving a straight septum which occurs in the overwhelming majority of instances, however not all. Third time septoplasty could resolve the obstruction so this is a consideration. Getting a second opinion would be wise as well. Further, looking into the other causes of obstruction must be done and ruled in or out. Make sure that the other causes are not present such as enlarged turbinates, sinusitis, allergic rhinitis, nasal valve collapse, nasal scarring/synechia, nasal polyps, and others.
To breathe through your nose, your nasal passage must be open and supported. The septum is the central wall between the right and left nasal cavity. When this wall is crooked, there can be obstruction of breathing because the air passage is narrow. There are other structures in the nose that also can obstruct breathing including but not limited to the turbinates, a mass (polyp, etc), or a narrowing the nasal valves. The nasal valves are at the the front of the nose and may be too narrow to allow air to flow easily or may collapse on inspiration when there is a loss of wall tension (bernoulli's principle). As there are many potential reasons one can have nasal obstruction, it is very hard in your case to say if your obstruction is from a "failed" septoplasty or from another cause without examining you. I would recommend you first return to your surgeon to voice your concern and see what your surgeon recommends. Best of luck with your breathing.