I ask for too many things

So yesterday I asked my dad if I could buy Audio Technica ATH-M50x. And he responded with a swift no because I already had SOL Republic Tracks HD from my birthday (2 months ago). And after 2 hours of screaming and arguing I can't buy the M50x unless I sell my SOLs. (btw im selling it for 90 bucks so contact me at manispeedx@yahoo.com). And today I was thinking about all the things I wanted. I want a USB splitter which doesnt sound too unreasonable. I want a mechanical keyboard. A pair of cheap earbuds. And Nike Air Max shoes. So 3 of the 5 things I wanted exceed 100 dollars. And tbh I don't really want new pair of shoes. In fact when my dad asked me on my birthday if I wanted to get shoes, I told him I didn't want to since I had 5 pairs of quality and working shoes. (2 Adidas, 2 Reebok, and 1 Vans). But my mom (since she did most of the screaming) was right. I ask for too many things, and its only at this age as well. I haven't asked for much when I was younger. I wonder what changed me to become like this? I think its things like this that made me drift away from academics and more to personality. I used to be a A+ student. Now im a B student and thats in average classes so I have drifted very far down from where I should be. And it angers me now that I think about it. I failed myself and made it much harder to achieve my dream of becoming an astrophysicist. To the point where I'm thinking of changing careers to become a game designer. But I dont know if that lifestyle is right for me. Either way I would enjoy it to the max (in Japan I hope!).