Breathing problems while swimming

Patient: Hi I have been going swimming for a while now. However over the last couple of months I have had difficulties when i am breathing out through my mouth while swimming. My nose starts to run and it feels like i want to get rid of some rubbish in my mouth. Then i practically have to stop because I cant breathe out. I have been doing breathing excercises through my nose. Breathing in and out and also I have done alittle pranayama. Could you please advise me?