What causes blood sugar to drop too low right after a meal?

High glycemic index. Foods (sugars, rice/white bread/potatoes/pasta) can rapidly raise blood sugar & trigger large release of Insulin which overcompensates & drops the blood sugar low. Mix good fats & protein with your meals & cut back on the sugars/starches should help stabilize blood sugars. See doc to be tested for "pre-diabetes" especially if diabetes runs in your family or your are significantly overweight.