I got involved in exercise classes at my local community college and exercised portion control (you can do this as a community member, if you'd like, or search for an affordable gym which offers classes included in the price. The college option is generally cheaper.). I started out with fitness jogging/running classes to acclimate my body to physical activity and then did step aerobics and weight training. Remember muscle mass does determine how many calories you can burn.
I also cut out soda and only would drink iced/hot tea (minimal amount of sugar if the tea was bitter as man made sweeteners aren't able to be digested well by most people) and water except for rare occasions. With only three 45-minute classes a week, it was a little bit slow going, but I managed to lose 20 pounds. Then, I started maintaining but still lost pant sizes.
I cut out sweets as often as possible but did not tell myself I could not have them as they make good rewards if you offer yourself *a piece* of chocolate or a *piece* of candy as a reward for a good week when it comes to portion control and sticking to your exercise plans.
What you choose to eat and drink has a HUGE impact on your weight. Portion control is hard at first, and you have to really pay attention to it as it's so easy to eat the amount you normally do, but it does work and you can lose weight on lithium.
I gain about 70 lb during my first round of chemo cause I was on heavy stoirds...I got were I craved sweets so I decide to eat oatmeal the malpe and brown sugar kind omg I ate it every time I got hungry and I lost it all in 6 months and I still eat it every day...that's my advise oh also told my doctor he said oatmeal was very heathy also...lol