Swimming & sinuses

This is actually not uncommon.  Swimming makes me sneeze, too (*pauses to wait for the "wait... you swim?" gasps of disbelief* ).  There's actually something called "swimmer's sinusitis", though there's definitely a difference between an irritation caused by pool chemicals and a true allergy to them.  Do you find that this happens regardless of in what pool you swim?  Sometimes the chemicals vary and can have more/less of an effect.  Some people use saline nasal spray prior to and after swimming and/or use a nose clip during.  I've also heard people say using a Neti Pot after swimming helps.

You probably need to learn to breathe correctly (my advice is schedule a lesson with Lisa Marshall). This used to happen to me also to the point that I quit doing flip turns because I would have water pour out of my nose later in the day (random water would just gush out...it was really gross). I used to get really bad sinus infections as a result. My Dr advised me to irrigate my sinuses after I swam (to get the pool water out) and then put me on Flonaise and it has worked wonders. Talk to your Dr if you continue to have problems with this.