Itune erased songs

I had to replace my hard drive and redownloaded itunes and upgraded to itunes 11, then today i bought a few songs off itunes and when i went to add them and i clicked sync and i noticed i went from 305 -310 songs to 283 songs but it did add the new songs i just bought. So i just lost about 25 songs and i am not sure which ones they are. How do i get them back? can i get them back? or did i just lose my money?

same thing also happend with my iphone 5 when i went to add new pictures on all my old ones were gone. I don't want to try to add anything to any device in case i lose what i already have on there.

so now do i need to figure out what songs i lost and have to go buy them all over again? how can i fix this?

I just checked some of the songs i use to have on there, it is making me rebuy them.