My Dress Barely fits an Im Tight on money?

You heard it, I gained some weight Bout 10lbs! Yeah I am On new birthcontroll And it messes with my weigh I'll Lose 10 pounds and gain 20, But Its in my belly area, I can Zip up the dress half way up under my bra, and If I work At it I can get it up all the way... I eather need a Good diet or something like spanxs but cheaper.