Help with new bad breath?!

Hello, I'm 17 and I am currently swimming on my high school team and our season is coming to and end in a couple of days. I have been swimming since november if it helps. Anyways, yesterday, I noticed that the top of my water bottle had a really raunchy smell to it, when I first opened it, it had no smell. This is the first time this has happened to me, even my friends started to notice it too. I also kept smelling it myself through out the day and it seemed like i was tasting during the day and while i was swimming after school. So today I went to the nurse to see what she has to say, she checked the back of my throat and she said I had thick mucus/slime in the back of my throat, she also said it was post-nasal drip but i don't really know. If ANYONE could help me out, I would greatly appreciate it. Lastly, I have not changed anything with brushing and rinsing my teeth, I always do it after breakfast and dinner. Nor have a changed anything with my diet, besides eating lots of banana peppers...Btw, my dad is a dentist, if that helps.