I Had An Allergic Reaction To A Pain Killer Eight

I had an allergic reaction to a pain killer eight weeks ago. My face especially my lips became very swollen and warm. Today I was on an airplane and all of a sudden the right side of my face starting swelling in the same way. I did not eat or drink or take medicine out of the ordinary. I was in the sun a lot over the last few days but am not sun burned. Any idea what is going on?