iTunes won't copy music to iPhone 5, But will to iPad 4

I'm new to iTunes but fairly tech savoy, I installed the latest version of iTunes and have ensured my iPhone and iPad are updated, I can't get my music from my PC to copy over the my iPhone, but it will copy over to my iPad. When I try to copy over to my iPhone it shows the music when I select "On This iPhone", but it will not play it from there and it's not on my phone. I have ran out of ideas, I would appreciate the help.