Nasal Stuffiness. If i understand your question it sounds as if you can breath through your nose but not through both sides at the same time. This is most likely related to enlargement of the turbinate tissue. It is very common for this to occur. You can try some saline nasal spray to start. Prescribed nasal steroids and nasal antihistamines may help. You also may need surgery to help reduce the turbinates.
May be normal. There is something called the "nasal cycle" where the structures in your nose that make mucous alternately shrink and swell. Usually this occurs every few hours. Most people are unaware of it. When it becomes problematic medications such as nasal steroid sprays can help. At all costs stay away from over the counter decongestant sprays such as afrin or neosynephrine which can make your nose worse.