Comment number does not increment

I am making a custom wordpress theme and when I add a comment to a post and retrieve the number of comments using get_comments_number() the number does not change.

I do know the function works because for the first comment that gets preinstalled with wordpress it returns 1. but somehow the number does not increment if I add additional comments.

Is there a way to manually increment this number?
Does anyone know what the problem might be?

Thanks for your suggestions!