It is nasty, and can cause a whole host of problems.
Do a web search for cleanse products, and follow the regimen. It's rough, but you will dfeel better that you have in a long time, and a nice side effect is weight loss.
The way to kill off yeast is to drink much (fresh as possible) grapefruit juice, secondarily cranberry. Acidifying your PH renders your body hostile to yeast, which needs an alkaline environment. Think: there is no such thing as orange wine or lime or lemon or cranberry wine, etc.
When I was 15 playing soccer (both before and after school) I got hooked on Dunkin' Donuts coffee, and drank barrels, and developed quite the yeast infection. Ick-ee.