How to receive data back on my iPhone?

I recently updated my phone to the current software iOS 5 from 4.2.1. After this, I lost all of my data. Is there a way to get my data from my sync?

Hopefully you backed it up before you synced. When you plug your iPhone in again, it will recognize it as a new iPhone because there's not data on it. Select restore from (whatever you named your phone).
Or I could be completely wrong and your data is still being uploaded to the phone as we type. You will know if it is because there will be a circular loading symbol in the top left corner. This is a new feature in iOS 5 you may not be familiar with.