Since your sugar is 112 and you do not remember if you have taken your
metformin 850 mg, and 3 hours have past, it is evident that you have taken your metformin.This is because your sugar level is normal now,and that you already had your lunch 3 hours before, so now the action of metformin is almost completed, and the
Carbohydrate.... sugar in your system(
glucose) is normal.You can wait till tomorrow,as this is normal.Always remember.... Metformin(850) is safe drug in
diabetes.. provided the blood sugar level is maintained above 150.You can safely repeat metformin(850) if level of sugar is above 150.Also note
An exercise like walking for 20 min ( in case you do not remember whether medicine was taken , will help a lot to reduce the blood sugar level, and also not cause a
low blood sugar level.
Ideally if you wish to control your diabetes and reduce the sugar levels, It is recommended to do exercise for 20 min(simple walking) after half an hour of taking metformin.... but after lunch or dinner and within 4 hours of taking metformin.
Hope you follow my advice and keep me posted on the effect of exercise after taking metformin(within 4 hours of consuming metformin)