Hi Anita,
In your campaigns, you could add the filter "Not Was Sent Email" in past 7 days. This would filter out all the people who have been sent an email in the past 7 days.
Alternatively, you can purchase an add-on to enable Communication Limits (you may already have Communication Limits enabled. You can check by seeing if you have a Communciat Limits section in your Admin). With communciation limits, you can set how many emails per week and per day any lead can receive.
Will