How to get my music back on my iphone? - 1

I just got a new macbook. I bought some songs on my macbook's itunes and I wanted to then listen to them. When I went into my iphone's music library all of my song were gone but the songs I had bought on my macbook. I went from having 102 songs down to only having 22. Please help! Thanks,
Emma

Added (1). What should I do to recover them? Is there a way for me to do that?

Since you bought the songs on a different apple ID, then the songs you bought on the old apple ID will disappear. What I did is made sure I had the Apple ID correct on my iPhone and mac book pro 2010. The reason they don't let songs travel over is because they would make less money. If a man or woman were to buy every song and pass there apple device around a room then apple would have lost over a thousand dollars in profit.