If you are using stock, download the google keyboard from the play store. Also hold down the mic next the space bar ubtil a menu pops up. Then click the gear icon then turn off auto replacent.
So weird, just all of the sudden while I was texting, the Samsung keyboard started changing every word I was typing, to totally different words, nothing even close to what I was typing. And I don't really like this Google keyboard cause emoji isn't on it why in the world would it all of the sudden start acting up?!
Mine does this too it's crazy. I don't know how to fix this. Can a dropped phone do this? My son bumped it out of my hand a few days ago. The screen survied so I wasn't too upset. But now OMG phone is going nuts. I swear that kid is going to mow lawns until he's 18 ...