Help! I need to lose weight!!

Okay so I'm 16 years old and I wieght abt 205 pounds. I have PCOS and it has caused me to gain a lot of weight. I'm on birth control to help regulate my period and hormones. It helped me lose a little bit of weight but not much. Does anyone have any suggestions on dieting or exercises that I could do that wouldn't be so costly for my mom? My family doesn't rly eat 'healthy' and I know any mom wouldn't go buy healthier foods just for me. So is there anything I could do without buying healthy foods? We have membership at a gym but we don't go much and I would rly like to start going but my mom won't take me.