It seems your blood sugar is sometimes on the low side to normal but for you that can be 'normal'. Can I ask why you've been taking your blood sugar if you're not diabetic? It's not something people usually do!
I guess the main possibilities I was looking at were: blood sugar, blood pressure, meds and/or supplements, heart problems (like blockage), or anxiety. And then, undiagnosed health problem.
So, again, I would record what you eat and what you are doing on a daily basis while noting how you feel: light-headed, jittery, sweating, etc. Maybe there's a correlation or maybe not but at least some reasons could be eliminated. And I would present all that to the doctor so he can get to the bottom of this. It's a puzzle, really.
What do you normally eat for meals and other times during the day?