gmail – running over my prayers

For some reason, I can not make edits, add words or phrases to my emails when I'm writing them. For example, you may have written "I need to take my exam." I read my email and I realized that I should have written "take back" instead of "take". When I go to "take" and try to add "re", the email does not let me insert "re". It is written about "take". Then I have to rewrite everything I've already written, which really sucks when it's multiple sentences. This never happened before. I do not know why it started, and I can not figure out how to prevent it from happening. Can someone give me the address?