how do I get my past purches i had on itues

I purchesed music in Febuary 2013 sence then I had to take my laptop back to factory state when I added itunes back on my computer and tryed to put music on my ipod shuffle it said I had to I was syncedd with another itunes library and i did what it said i had to synced it again but when i did that it took the song i had purched in Febuary off my iopd shuffle and i would like to put them back on my ipod thank you.