Because donations are recorded against your email address, any donations made via the email address you register with will appear, even if made before you registered.
To view your history (inlcuding accessing old receipts):
On the right of the My Givealittle screen (or in the Hamburger menu on mobile devices) there is a menu option called 'Transactions'.
Within 'Transactions' select 'Donations Given' or 'Pledges Made'.
To access old receipts, click on the document number in the first column of the transaction listing: