Why won't TurboTax allow me to type in my student loan interest myself? I click "Type it in myself" and immediately starts rechecking my info for needed edits

It sounds as if it is entering Review while you are in the Education section.

It may be best to refresh the information and make sure nothing it hung in the cache. I would recommend to back out of this section, back to the main Deductions and Credits screen, then sign out of TurboTax Online and clear your cache, or log in with a different browser. Return to the Education section and see if it will let you type in your student loan repayment interest. 

If you are using Turbo Tax Online, the most likely reason for boxes/buttons that don't work or not being able to enter information is that something in the web browser is not displaying the page properly. There are directions in this TurboTax Help article to clear cache and cookies. You will want to follow those instructions, then close your browser, reload it, and log back into TurboTax. 
 

Another way around this is to simply use a different web browser.  You can select from Google Chrome, Mozilla Firefox, Internet Explorer or Safari.  If you need to install another browser, be sure to go to the trusted home site for the software for  security reasons.