Yes, these symptoms could be side effects of your medication. Tryptomer (amitriptyline), even at a low 10 mg dose, is known to cause fatigue and can sometimes cause heart rhythm changes or an irregular heartbeat. Nervijen (Vitamin B12) is unlikely to cause these symptoms. You should not take any new medicine to treat these symptoms yourself. An irregular heartbeat requires immediate medical attention. Please consult your doctor or visit a clinic promptly for an ECG (heart trace) to evaluate your heart rhythm. Your doctor may need to adjust your Tryptomer dose or switch you to a safer alternative for migraine prevention.