Why is it always so hard for me to breath through one of my nostrals?

Septal Deviation: The most common cause of one sided nasal obstruction is septal deviation, though sinus disorders and grows can also cause obstruction. Septal deviation is easily repaired with surgery. You should see an ENT doctor for an examination.

It's a natural cycle: You naturally cycle breathing through predominantly one, then the other nostril as tissue in one swells, decreasiing air flow, then goes down as the other does the same. This happens every couple of hours or so. If you are pregnant, you already feel somewhat congested because of increased blood flow to the sinuses, so this may feel more pronounced.

Broken Nose? Septum?: Difficulty breathing through just one nostril is often related to a broken nose and a deviated septum, the wall separating left and right nasal passages. If injured, a septum may shift to one side. A nose specialist can tell. The good news? It’s probably correctable. A routine 30-minute surgery to straightening the septum, improving air flow, has been done for over 100 years and is very popular.