The pill...immune suppressant?

Just curious if anyone else has had this experience. 

I went on the pill at the end of 2011 for my skin. From March 2012 to November 2012 I was constantly sick with sinusitis. Doctors said I had allergies, but blood tests always came back negative. I even went to an allergist and did a skin prick test with the usual allergy culprits as well as a few extras from my work environment and l came back negative. In 2013 I had an operation to widen my sinuses to help them drain better. Did not help very much. Every year from March to November I was constantly sick.

In March this year, I decided to go off the pill. In the past 4 months I've only been sick with a cold twice and both lasted no more than 10 days! 

So it seems the pill was somehow suppressing my immune system!! Has anyone else experienced this???