I mailed my package on the 11th and its not there yet!

I am pretty upset! I mailed my buddy - Sherry M's package on March 11th. Thank God, I have delivery confirmation on it, but it hasnt moved from its destination since the 13th! How long do we give the post office before complaining? I didnt forget, sherry! it is on its way, but if I send another package, what happens if the first one arrives? arrgghhh, almost as frustrating as not getting a package on time, delivering one not on time is just as bad!!