My HRM dilemma

DreBeauty

OK so I have tachycardia commonly known as an irregular heartbeat...it's always rapid even when resting. I've gone to several doctors, worn every type of monitor and taken every kind of test and the doctors have no clue as to what is causing it, but they do know it's hereditary because my mom has it as well. My problem is that I don't think I'm getting an accurate reading from my HRM because my heart rate is so bonkers...I either get a really high reading or an extremely low one (and I know I'm not that fit to have only burned 71cals after jogging for over an hour) I really just want to know if anybody else has this condition and if they find using a HRM as useless as I do and if you have come up with any other method of calculating cals burned please let me know. Thank you.