Get to your keyboard...
1) Tap and hold the microphone button...new menu pops up
2) Tap the "gear" settings button
3) Tap "Predictive Text" option...then TURN ON
4) Check the box next to "Personalized Data"...that should keep any words you have used once you have checked them after typing.
Or you can simply turn it off and it will keep anything you actually type.
It's your choice.