Birth control... Weight gain?

Zerenity
My doctor put me back on birth control due to my cyst. I haven't taken it in almost 2 years. I've lost quite a bit of weight, and I would like to keep it off. Anyone know of tips to help me? I'm on a diet, that's definitely healthy and meets my needs, I just don't want all this effort going to waste./: 
Thanks so much.(: