iPhone not showing in Music App - why did they change this???

I don't understand why Apple keeps changing things that didn't need to be changed! It used to be really easy and simple: connect my phone via USB and put the music I want to select from my computer onto my phone. Now I plug the phone in and the Music app doesn't register it. I've tried all the 'helpful' tips and nothing works. All I want to do is select various tracks I've created myself on my computer and upload them onto my phone but that's impossible because Music doesn't allow the phone to connect to it. What did they change to make this once simple operation impossible!? And why!!??? SO ANNOYED!