Age20 hr is always over 100bpm ecg comes back normal, what could it be? otherwise fit,healthy, active and hydrated?

Possibilities: 1)Amitriptyline increases HR 2) you could have the syndrome of inappropriate sinus tachycardia 3)you could have increased HR because it's being checked (conditioned reflex) 4) you could have an incessant atrial tachycardia - To sort all these possibilities out, have a 24 hour monitor (Holter) done - it will show what your HR is during sleep, on average over 24 hours, and when you have symptoms.

Normal maybe?: A normal heart rate can be up to 105 beats per minute. If it is over that rate then you need to consider other causes such as anemia, anxiety, medications, hyperthyroidism, general poor physical fitness, and cardiac arrhythmia that may not be detected on a resting EKG. You are probably ok but if remains a concern, see your doctor and tell him your concern and he could do further testing.