All indications ,to me, point to a pre-diabetic readings, even your fasting was 95 < less than 100 mg/dl .
I would now buy a self-test kit for your hbA1C, called A1C Now , made by Bayer at Walsmart for $29.99 US or at Walsgreen for $39.99.
Follow instructions , then within 10 minutes, voila the result is there.
A bg of 146 kinda tells you that maybe cereal is not the best breakfast for you.
Fiber one has lots of carbohydrates (it says rite on the side of the box "Nutrition information"), and it is carbohydrates that raise your BG.
Good to catch this early and then you can modify your diet and activity levels and maybe stop it progressing.
Focus on lower carb foods. Exercise daily. Normalise weight.
So, it has been peaking at about 200 45 minutes to an hour after I eat, but within 2 hours it is usually below 140. Waking up it is always between 95 and 100. I just went to the doctor and she says I likely have some "insulin resistance." Which is strange because I am 29 and thin. She said it is probably stress.
Guess what despite what the TV says diabetes is not just for fat people. as I understand it ANY reading over 200 puts you as diabetic. Your BG returns to normal 2 hours later meaning your phase 2 insulin response is still working (your pancreas is still making insulin). You need to make chainges or you will wear out your pancreas.
With your current numbers your best bet is exercise, and diet will work. Diet as in life style change not "going on a diet" Diet.
Get a meter test before you eat and 1 hour after, if your BG rises more than 40 pts (US measure) or goes over 140 time to rethink what you eat. We do know that carbohydrates (carbs) raise BG, ALL carbs raise BG whole wheat raises carbs, so does a bowl of sugar your body does not care what carb you eat they all (carbs) raise your BG.
you don't take insulin?
The 200 @ 45 minutes is abormal and even 140 is on the high side of 'acceptable'.
Stress does not give you hgih blood sugar. Sorry, your Dr is doing you a disservice by labelling it as stress.
Given you are thin and young, this should be watched closely as it may be what is called adult onset type 1 (a slower onset type 1).
In any case, to minimise the peaks, you should be minimising your carb intake (and test after meals to find which foods don't send you so high). You could also try walking straight after eating which can also help bring blood sugars done.
Fasting numbers between 95 and 100 are also higher than normal. truely normal is < 95 fasting.
Have you had your HbA1c tested?
I beleive you should try diet and lifestyle measure to try to reduce your numbers. If this doesn't work and your Dr doesn't take you seriously, a second opinion is recommended.