Dont dose if your tired, cause your prolly gonna fall asleep, try in the morning after a cup of coffee or something. You also need to be relaxed, not only focused. So if your walking your dog then its prolly why it doesnt work. Sit on a chair or lay on your bed.
Maybe you got cocky thinking that it would work for you each time, you skipped a step in relaxation or concentration, and now it won't work. Go back to the basics, how you originally got a dose to work in the first place.
these doses will not work while trying to perform other tasks.
you need to be in a dim or dark room, relaxed mentally and physically, and be focused. then they will work almost every time. keep trying.