I am currently trying to lose weight - always been at a healthy weight but I gained a couple of kilos off hypo treatments a while ago and I'm slowly trying to get rid of it. How many hypo treatments do you eat in a day? I found that I was getting hundreds of calories off juice and lollies, and while trying to cut back on that is good, it's impossible to stop eating them completely or to know exactly how much you will eat. Steps I have taken include
1) try to run my blood sugars slightly higher to avoid lows (= avoid hypo treatment food)
2) cut back on planned carbs. I used a calorie calculator on the internet to help plan out what I would eat (my goal is somewhere between 1200-1400 calories a day including hypo treatment - the broad range leaves some wiggle room since I may need different amounts of sugar on different days)
3) exercise - this is the tough one for me since it always makes me low, which means eating, which completely negates any gains from exercise. So if like me you struggle to exercise, don't have a snack beforehand, instead adjust your insulin (easier with a pump - set a temp basal. With MDI you can reduce your basal, and/or reduce your previous mealtime bolus). I've been trying (and failing!) to do 30min walking every day. Some days your blood sugars just won't allow it, and that's ok - just try your best and remember some exercise is better than none, every little bit counts.
I have heard people say that insulin causes weight gain but I'm not sure how true this is - I lost weight AFTER my T1 diagnosis (no DKA) and remained at the same weight for a couple of years. I know my weight gain was caused by eating too much.