My music got deleted from my iPhone?

I have an 8gb iPhone 4 I had all of my music on my phone the previous day then i tried to play a song but there wasn't any music except for music i bought from iTunes then i went and synced with itunes and it said that I had 3.5 gigs of other data on my phone (p.s. I really only have 6.4 gigs total of the 8 gigs) and its never been that high. When i tried to fix it I accidently deleted my playlist from both iTunes and my phone but I made a new one just like the old one. The new playlist is the same size as the old one and it won't sync because of the other data on my phone taking up too much space. How do I fix this problem?

You can use a 3rd party software like this Data recovery to retrieve the deleted songs from your iPhone, it worked fairly well for my iPhone 5.