Problems with my mic, I think it's the computer.

Hello, I've been having a problem with my computer for a while now. When I speak to people my voice at first is normal. But as I continue to speak my voice cuts out and becomes super quiet. I don't think it was like this when I first got my computer but I am not sure. Could this be a settings problem or do you think it's related to the computer itself? Is there a way to fix this?
Thanks.