What Causes Swelling In The Lip?

Hi, I squeezed my lip and some tiny cream colored stuff came out. I put some lip balm on and then went for a 2 hour walk. 15 minutes after i got home, i noticed my lip started swelling. I'm not sure if that i didn't notice because it was so cold outside, but now its the next morning and i took some Naproxen that i already had and the swelling on one side of my top lip is spreading to the other...my bottom lip is still normal.
Can you please tell me how to stop the swelling from getting worse and how to treat it?