Hello dear,
Metformin causes following side effect:Abdominal or stomach discomfort
cough or
hoarseness, decreased appetite, diarrhea,fast or shallow breathing
fever or chills, general feeling of discomfort, lower back or side pain
muscle pain or cramping, painful or difficult urination and sleepiness.
So it can cause fatigue and cramps.
First you should confirm your diagnosis of
diabetes by blood glucose testing and HB1Ac.
You can also measure blood metformin level: it should between 1-4 mg/l in person taking metformin therapeutically.
In overdose level is between 40-120 mg/l.
So check blood metformin level to prevent its side effect.
Hope this may help you.
Dr. Sagar