Any Tips?

Hi I'm 15 (16 in October) I am in the 10th grade and I am a little over 300 pounds I was always chubby but when I hurt myself in the 7th grade I couldn't do much for myself which caused me to over eat and ever since then I been pretty big I love myself of course but I recently had my physical and my doctor said I'm ok it's just I need to lose weight and my ma doesn't buy healthy foods so I'm stuck eating what's in the house and every diet I've tried sends me to the hospital I wanna lose at least 30 pounds before January and honestly i just wanna be able to go into a store and not have to put something back because I'm too big for it or it won't look cute on me because I'm big