Has anyone taken this for fatigue and had it work for 3-4 days and then stop? My doc doesn't have much experience with it and I'm trying to figure out what this means. I started at 100 mg, which worked ok for about 4 days, then stopped working. I just doubled the dose, but only getting a little push in the morning, then getting sleepy in the afternoon. Some people say it takes a while before it starts to work. My doc said I'd know in 2-3 days. Not much solid information available. I'm trying to figure out if I need to stick with it, and if so, how long to keep trying.