I had balance problems also, they went away after about 3 months.
Also, about the weight gain you just have to stop eating even though you are hungry. Write everything down and when you reach the max calories for the day for your height and weight you can't eat anymore. Eat proteins and fats with each meal, and fiber to keep you full. I am hungry some days, that's just the way it is if you don't want to gain. Nip it in the bud before you put on 30/40 pounds like some of the others on Lithium.