Lost music,

Hi, can anyone help? Iam an iPhone user and over the last few years bought a lot of music for my device from iTunes. I recently found an iPad I had from my old employer (they gave it to me when I was leaving) which got locked as I had forgotten the password I used two years ago, I got it unlocked and changed my Apple ID on both my phone and the iPad to a new one. Now my music is gone and my apps which I downloaded on using my old ID will no longer update. What do I do.