Hi, last week i was perscribed 20 mgs of adderal xr, i took it for a few days, i felt great on it and all but i had trouble sleeping at night so itook a break today, but ive noticed my heart rate is at about 90bmp still and i dont know what my normal resting heart rate is, im a male, 17 years old, 135 pounds, and pretty healthy..is 90bpm normal