Why Won't My iPod Touch Add Music?

I have been experiencing this issue for a while now and am getting increasingly frustrated the the point where I no longer care to own an Apple product of any kind. I have a lot of music. I store all my music on my laptop and plug in my iTouch occasionally to put new songs on there. However, any time I drag my songs over like normal, they don't show up on my actual iTouch. My laptop displays a happy list of all the songs that should be on there, verifying that the songs are in fact on there, but they are not. When I tried to add new songs today, my iTouch decided to delete everything except for what I had purchased directly from that device leaving me about 3000 songs short of what I should have. My laptop says the songs are on there, however, the amount of remaining GB free has altered dramatically from around 5 GB free to now over 23 GB free because my music has completely disappeared from the device.

My iTouch, laptop, and iTunes are all updated, and my iTouch is set to show all music, so I don't see why I am experiencing an issue like this. All I want is to able to listen to my music on the device I was promised could do that. If your product cannot function the way it was intended to, then I do not see any reason to trust your merchandise in the future.