Lost tons of songs!

Had to restore ipod, didnt allow me to transfer my purchases before. Now I have lost tons of songs. Since I had an iTunes giftcard, i thought that i might as well just rebuy the songs. But when I try to purchase these things back, it says that I already bought them. I clicked on the purchased button in my itunes store. Nothings happening. I refuses to show me what I have purchased. What should I do?