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):
If you are on a desktop or laptop machine, on the right of the My Givealittle screen there is a menu option called 'Transactions', and under that 'Donations Given' & 'Pledges Made':
On a mobile device it looks like this:
Access the list and then to access old receipts, click on the document number in the first column of the transaction listing: