Music app regularly fails to load (crashes) [3GS 5.1]

Hello everybody, I read a lot of stuff about this, but nobody that had this issue seems to have fixed it somehow, so I am opening a new discussion.

I have an iPhone 3GS and I have just upgraded to the last iOS firmware, the 5.1. Everything went smooth, I recovered with the backup from iOS 4, and everything seems to work, except from one essential thing: the new Music app, which is supposed to be the new version of the iPod app. Whenever I tap on its icon I get a white screen (with the empty blue bar on top plus the tiny status bar with signals, time and battery on the very top) for like 1 second, then it crashes. And this happens no matter what, I tried to reset, restore, unsynch music, resynch it.

Now the weirdest thing is that I didn't notice it at first, because when I plug in my headphones, which have the little button to control song switching and volume, it plays normally. It doesn't crash or stop. Same thing when I use the controls on the Lock Screen, accessible by double-clicking the home button while on the Lock screen.

Another weird thing is that when I tried to unsynch all music (delete everything from the iPhone) by unchecking the "synch music" option on iTunes, it left 5 songs from a playlist, but they weren't even all of the playlist. I don't think it is just 5 random songs though 'cause I have more than 6000 songs on it. And they didn't show on iTunes in the "Music" folder under my iPhone on the left tab. But they did show up in the "Info" inside the iPhone, is said I had 5 tracks. Infact if I pressed play with my headphones or Lock screen controls, it just went on random play just with those 5 tracks.

Anybody have any idea of what I should be doing?