How to add music from my iphone to the computer?

Hi, I recently cleared my laptop and put everything back on again, but I accidentally didn't back up all my music. I want to add more music onto my iphone now but when I try to sync it its asks me if its okay to remove all the music which is already on my iphone and I don't want to really loose all that music, does anyone know a way I can get all the music from my iphone back onto my computer?

I had the same problem, phoned apple and they told me only music purchased through itunes could be copied again but there are programmes out there designed to copy music from iphone to pc, have a look on youtube for tutorials.