This is normal and is known as the Nasal Cycle, where one nostril congests slightly to filter, humidify and warm the inhaled air whereas the other nostril dilated to allow smell sensation as the odour molecules have to reach the uppermost portions of the nose for them to be sampled by the olfactory mucosa so that your brain can perceive smell. Every few minutes, the nostrils reverse functions in cyclical fashion. However, due to the onset of winter and the ambient atmospheric pollution, this congestion may be more, thereby becoming noticed by you. The best solution for that is to do warm saline nasal washes(similar to Neti wash being taught in Yoga). Just make sure the salinity is a little more than that of your tears(hypertonic) and add some soda bicarb to buffer this solution to avoid the stinging sensation.