HELP!! weight loss and gym

So I'm only 16 and I need to lose weight due to a medical situation I'm about 15 kg overweight.. I've been think of joining the gym but I'm having a operation in the beginning of march. I only get $30 a week and I don't have a job and gym membership is about $62 a month so should I save up for a couple of weeks to get enough money to pay for it + registration and join after my operation?? And I already eat relitivley healthy it's just I don't excersice