You definitely want to get a tool designed for that purpose. you're going to find that Excel doesn't scale well at all for what you're trying to do.

Take a look at Salesforce perhaps (although it's expensive), or some other solution like SugarCRM, or one of many dozens of other tools. For example: http://alternativeto.net/software/salesforcecom/

A lot of them are painful to use, but they're less painful than Excel.

The most important things you need it to do are keep track of the customer data, keep track of contacts with them, and allow you to schedule events, like calls and emails.

As you get more sophisticated you might want to start keeping track of lead value and potential, but for now, you'll just need to get people in a system that works better for you.