Ocean or pool causing vaginal imbalance?

3 months ago I moved to FL and started swimming every day in our pool without problems. Then I went into the ocean and got a severe vaginal imbalance causing white discharge and itching. I treated with OTC monistat which took care of surface itching but didn't clear up for 2 weeks. 
Now I swim less, but went in the ocean and pool in the same day. 5 days later I had a slight white discharge, been eating yogurt constantly, now my vagina feels like the Saraha desert. Even with sexual arousal and climax I am still dry.
What is going on? How do I prevent this?