@sara859 - Hi! You will need an experienced endocrinologist- such as at a major university, where they see a large volume of patients.
Your body seems to overdo it when releasing insulin after a carb meal. High insulin will cause the glucose drop.
I’m aware of one condition that could do this. There could be a tiny, benign growth in the pancreas that produces insulin in excess. Often they are not seen on CT. It’s called insulinoma- it is NOT a cancer.
I hope you get some more testing soon so you can get treated.