Head congestion after swim

I have been swimming in the same indoor pool for the past five years and have never had any issues with the water quality.  However, over the last month every time I swim I end up with congestion, running nose and sneezing about three hours after I finish up.  The pool claims that they have not made any changes to their chemicals.  To further complicate matters, I had the same symptoms after an OWS last week.  I am just dealing with over sensitive sinuses or I am I becoming allergic to swimming.  Any thoughts?