Ongoing data input

Please excuse me if this function already exists (please tell me if it does):

How can i create my fields such that i can continue to "add" data to a created entry. For example, let's start with this entry:

John Doe
SS#000-00-000
1/28/04 Charge $23.00

Now i want to created simple field forms so i can go back and insert "2/3/04 charge $44". Let's say this goes on indefintely for an entire year so i can capture all the charges John Doe has accrued. I know i could just make a text box and keep modifying, but how can i do it so that a new "field" is created for each new Date and Charge?

Thanks for your help.