Hi there, I've had some symptoms like what you're experiencing here.
Usually when my sugars just rise up without food, it's due to some of these reasons:
1. On mornings where I would skip breakfast, my sugars would just rise as my body broke down fat/whatever to get the energy it needed to keep going (it's like hidden sugar from nowhere and it would always send my sugar from like 118 to 220-290 depending on my morning activities).
2. If I exercise and get dehydrated, or if I exercise for a fairly extended period of time, my sugars just go up and up. When I did wing chun kung fu classes which were 2.5 hours including 30 minutes of exercise (that's a long time to keep moving!) my sugars spiked up to 500+ every time til I managed a system which involved giving myself shots and keeping hydrated as much as possible while exercising. Even light exercise could get my sugars up if I had adrenaline pumping.
3. If I am getting STRESSED to **** by something or if I was feeling a little off (you know some days you feel off but not quite sick) my sugars would rise up. My sugars in the last 4-5 years (when I was in college) would be all over the place when times got stressful.
4. If I had a schedule change or a medication change or a long-term change in activity my need for insulin would change (and thus my sugars would too, going up or down or whatever).
From what I see that you're describing, your sugars went up after you ate some food that you don't usually eat for breakfast, yeah? Sometimes when I have a bowl of cereal for breakfast which is a bit "denser" (in terms of carbs/cup) than other cereals my blood sugar will just shoot straight for the moon. I found that when I was on shots I really had to keep my meal sizes (in terms of carbohydrates mostly, with the other stuff like veggies or meats being a little more flexible) very consistent. When I would change things up my sugars would go all over the place.
As for when your sugars rose after a bit of weight lifting, that was probably just what your body does when you exercise. Exercise will get your sugars going up and, depending on the intensity of the exercise, you may need to give yourself varying amounts of insulin and consume various amounts of water (with electrolytic/energy drinks as necessary depending on how much you are sweating) to keep your sugars stable.
But yeah, as a basic response to your main consideration of blood sugar rising when you don't eat food: That's your body breaking down fat (and sometimes muscle, gotta watch that) in order to get the glucose/energy it needs to keep functioning throughout the day. If you keep skipping meals and fail to eat enough you will screw up your metabolism which will hamper your ability to lose weight AND will mess up your blood sugar control. Basically whenever you don't eat you're probably going to see your sugars rise several hours after a missed meal, and if you don't eat enough each day you're going to make the problem worse. If you're dieting or trying to lose weight right now the best way you can help it is to make sure that you eat three meals a day, making sure to control PORTION SIZE and keeping enough fat and protein and carbs in your daily diet so that you don't become sick because of malnutrition or under-eating.
Since your doc sounds useless for what you're trying to do, call around and try to find some nutritionists in your area. They're usually classified as specialist doctors (extra $ out of pocket) but they can give you a diet plan that will meet your nutritional needs (for energy so you can exercise and still function each day) but will still cut out all the bad stuff so you can lose weight (namely cutting the excess calories out). Make sure the nutritionists you work with have worked with diabetics before because you don't want some nutjob that tries to put you on the Atkin's diet or something!
Hope this helps a bit.