What causes the nose to get bigger and thicker in a teenager? (Photo)

It is difficult to know exactly what is causing the changes to your appearance as it could be attributed to multiple factors.  Changes in the nasal appearance can be due to growth and maturing as an adult, hormonal changes, temporary swelling due to things such as activity, diet, etc. 

The simple answer is that your are maturing into an adult, and your male hormones are making your skin and glands thicker on the nose. This is of no medical  concern  - have a look at your parent's noses as this will give you a clue as to how you might look in the future!