I can't stop crying pls help

Okay so like I got a really, reallt good and expensive gift for my birthday right? Like a gift that most people would be going crazy over. But I can't stop thinking of reasons on why the gift wouldn't be good for me and i cant think of anything but one thing I'd use it for. And the worst part is im greatful for it I really, really am but I just cant help it and I feel so bad and I cant stop crying and I feel so ungreatful WHEN I'M NOT! It's great! 

Why can't I just be like other people and just think positive?