I ordered an iphone case from amazon? - 1

I received an emal that it shipped Friday the 21th 2013.It's now Tuesday and on the USPS tracker it shows it hasn't even been accepted yet. Also when I enter my tracking number into the website I get this message

Delivery status information is not available for your item via this web site. A return receipt after mailing may be available through your local Post Office.

Should I be worried?

I'm going through the same thing 'cept it says it was delivered but it never came I think something might be wrong with there site right now?