I found the fix guys.
Go to Menu>Settings>Launguage and Keyboard>Samsung Keyboard
Make sure XT9 is checked, click XT9 advanced settings, then select auto-substitution is checked.
If you look down at the bottom where it says XT9 auto-substitution click on it, and it will show you which words it will automatically substitute. One of them being "i" which will be substituted with "I". You can also add other words that will automatically be substituted.