Maybe your insulin regime is not ideal. How is it dosed? If it is on sliding scale it can be very hard to control. Basal insulin combined with mealtime dosing based on what you actually eat can give better and easier control.
Eating lower carb reduces the requirement for insulin and means you can take less and therefore control the rollercoastering.
All of Waverider's advice is excellent.
Have you been educated on diabetes control and management? I'm not talking about medication but about the lifestyle changes one must undertake in order to prevent the roller coaster glucose levels. Without knowing your background or what you're doing to control and manage your diabetes a few questions comes to mind.
1. Have you taken a diabetes class? If not check with your local hospital whether they offer one. Most do. Your doctor may know of one too. Here you can get a basic understanding of how to control and manage your diabetes.
2. Are you following a type 2 diabetes diet? Along with avoiding sugar and sugary foods you need to limit your carbohydrate and starch intake as these foods quickly turn into sugar after eating. For example, potatoes, white rice, foods made with white flour - breads, crackers, etc. Eat lean meats, fish, poultry and vegetables. Avoid snacking before bedtime. Use Google search on 'good carbs vs bad carbs' and the Glycemic Index to understand proper nutrition. If you need assistance in this area ask for a referral to a diabetic nutritionist/dietitian. Again, most hospitals have one or more on staff.
3. One must maintain normal body weight, exercise 30 minutes daily, control your cholesterol and triglycerides and blood pressure. Walking is very good, not strenuous and does help to lower glucose levels. Don't overdue it at first and try to gradually build up the pace as if you're late to catching an airline flight.
Post back to this thread if you have further questions. Good luck