loosing weight

I need help asap! i am 8 months postpartum and my birth control i was on after having my baby made me gain 20 lbs. i used to be 130 but now im 170!!😭😭😭 my boyfriend tells me im beautiful every day but i get upset just seeing myself in the mirror. can any one give me advice on how to start losing weight and if a gym really does help lose the pounds?