What are allergies?
The human body is incredible. It has all sorts of ways to defend itself against foreign invaders. When something gets in your nose that doesn't belong, you sneeze. Your eyes water to flush out alien objects. Your skin swells to combat invasions such as a bee sting.
But sometimes your body gets just a little carried away and overreacts. It thinks that something is attacking, when it's really not, and it goes a little bonkers.
All around you there are things that can get on or in your body. They don't do any real harm. But your body may react to them. Some people's bodies react to dust or cat dandruff (called dander). In your case it's pollen.
In the spring and fall, primarily, grains of pollen float through the air from trees and flowers. Your body has an oversensitivity to pollen. When pollen enters your nose, your body believes it's under seige and starts to manufacture antibodies to attack. The antibodies make other chemicals, such as histamines. The work these chemicals do is generally valuable. But in this case, the histamines unnecessarily make the inside of your nose swell so that it's hard to breathe, your nose gets stuffed up, your eyes begin to tear and you develop all the symptoms that you were describing.
People have always had allergies. If yours are really bad, your doctor may prescribe an anti-histamine to combat your body's reaction to pollen. But, it's far more likely that your best bet is to keep an extra tissue around and wait for allergy season to pass.