Hi Sarah,
I am a little baffled
to say the least, as if your are on a network it should show under your airport connections as the network you are connected to.
Click the airport icon then select (
join other network ) as my screen shot, when the new box opens click (
show networks ) does yours now show up?
1) If yes select it, does it now show when you click the airport icon?
2) If not then click cancel and go back to join other networks then enter your networks name and its pass key.
What are the answers to (1) if no then what happens with (2) does it now show under your airport connections.
Also must ask if this is a USB WiFi device and which country you are in?