Adding text - changing one changes all

I am trying to add captions to my video. If I add a line and then cut it to change the text for the next section of audio, the text in the previous line also changes. How do I get it to treat each one as a individual item? I don't want to have to add a new text box each time, because then I have to reposition it and make sure it is in the exact same place as the previous line, and that's just a pain.