I feel you my friend, and I know what it's like, so What i did in that situation is wait till summer, it right around the Conner, and pulse in the summer you'll have way more time to play with the dog and house train him, and simple things like that. So my best answer is wait till summer and you'll have a better chance of getting a dog!
Also make sure you really convince to your parents that your responsible, do something like, if I can prove to you by doing something that will be able to show them that you are responsible!