Does simply starting medication help with losing weight?

Hi 26F here! so Ive been struggling with weight gain for the last few years now. Ive noticed I can barely eat anything without gaining.. Like I can eat less than half of what everyone else eats and still be the one who adds on weight. I just this week discovered a high TSH at 14 for the first time ever.

Im hoping to start medication once I get to talk to my doctor... so Im wondering if it's normal to lose weight when starting medication, but without changing the way I eat atm? I already eat so little so I can't handle eating less to try to lose any kilos. Asking because my joints have started aching a lot due to carrying more and more weight and Id like to get it more back to normal..