It's perfectly normal to put weight on as your body has been starved of energy for a while, the cells are trying to replenish their stores, the focus should be on feeling healthy and getting your strength back, I too have put on weight, however am not too bothered as I eat healthily, I run 2-3 times a week and gym twice a week, and would rather be a healthy weight than pre diagnosis weight which was quite underweight.
When trying to keep weight down focus on the calories being eaten so keep track of these, try to keep your control as stable as possible too as running high will make you more hungry and try to not over treat the lows, add exercise where ever possible and drink lots of water. This should help stabilise your weight and help you lose the extra too