itunes account with old email address and now I can't get access to music?

Hi. I set my itunes up years a go on an old work email address,now my apple ID is a different personal email address. When I got my new iphone, the apple ID is my personal email address so my itunes account is now not linked. If I change my appleID on the phone I can see my music but then all my apps etc are all on my new apple ID and not my old email address! Hopefully that makes sense?!

How do I get all my music from my old itunes account on to my new phone with a new apple ID?