The most obvious reason why your campaign hasn't sent any emails to the new contacts is that its status is already completed before you added the contacts. If a campaign has completed, it won't do a thing anymore.
If that's the case, what you'll need to do is to resubmit the campaign again. So just edit the campaign, go through all the steps without changing anything, then click Submit at the last step. Your campaign will rerun and will send the emails to the new contacts that the campaign recognizes. That means that the campaign won't send the emails to the contacts that the campaign has already sent emails to beforehand.