Hi
@Porffor
I think that one reading after a high carb breakfast is a bit too early to draw any conclusions. So as you suggest, a bit of further testing, combined with a food diary, looks like the way to go.
A reading of 3.9 is no cause for alarm, unless the patient is on a medication that causes hypos, such as insulin or gliclazide.
Many non diabetics see readings in the highish 3s throughout the day.
My suggestion would be to test before eating, then 2 hours later, and then at any time you feel symptoms.
Combined with a food diary (don't forget the portion size/amount of carbs) will help to quickly build up a picture of what is happening, and show you where to make adjustments to your food intake.
Hope it all goes well, and please come back and let us know how you get on?