transferring music from iphone to itunes

Hi,

I am having problems with my Macbook pro and transferring my music on to Itunes. I think the reason is because I had another library on my previous computer. This is very frustrating because I own an iPod touch, iPad and iphone and all were downloaded onto my previous computer. HELP! Also I have just purchased the software Lion does this mean I'll have to convert all of my apple devises.

Thanks

Angie