I gained 20 lbs when I first went on insulin. I was taking too much insulin which made me hungry so I gained weight. I decided to back on my oral meds to see if I could manage my blood sugar w/o the insulin. It didn't work. In the meantime, my test results (GAD antibodies) came back positive for type 1 diabetes. I had no choice but to go back on the insulin.
However, I made sure to keep my insulin levels low and match it to what I ate. I did not just start eating whatever I wanted because I was on insulin which I had done before. I went back to the low glycemic index diet and started going to the gym. I train 3X a week w/ weight + cardio and 3-4 x a week just cardio.
My blood sugars have dropped dramatically and I no longer take my noon insulin on the days I do weight training. I've gained 3 pounds of muscle and can now run on the cross trainer for 15-25 minutes.(depends on which day weight day vs cardio days) I could barely do 5 min when I started. My goal is to do 20 mins on the cross trainer on the days I also do weights. I only started my excercise 6 weeks ago. I wish I'd started years ago!
You CAN lose weight on insulin but you will have to work at it. I know this isn't the answer you wanted to hear, especially if you've been on byetta. The weight just drops off w/ that stuff. (been there!)
Educate yourself on the best type of diet. I personally think the low glycemic index diet is the best for diabetics. There are many books or on-line sites that you can read up on this. It will show you what type of foods to eat that won't spike your bg. (slice of white bread vs chunk of whole meal/multi grain, apple vs grapes, banana vs orange) Do you know which is the best one to eat? Which one will release more slowly and keep your bg level steady? Which foods are "free" virtually no calories + no effect on your bg levels.
Get your dietitian to help you. They will have a vast knowledge of books, recipes and tips you can use.
Oh, take it one step at a time. Don't try to change everything all at once, it will just overwhelm you. I've been working to get where I'm at since 2007. It's a long, slow process of learning what works and what doesn't.
Good Luck!