Hypothyroidism. Please please help.

My tsh level shown is 6.59. So, my doctor told me to take thronorm 25mcg. I am taking this tablet since August 2020. Last month I took thyroid test, and my throid value reduced to 3.59. But I am getting heart palpitations continuously for day and night. My back head and back neck is pulsating when lying in bed. Took ecg, report shows sinus tachycardia. Kindly inform if this could be because of thyroid problems. I do not have any other medical problems. Please advise me as I am really getting irritated because of heart palpitations as I can sense my heart beats too fast and pulsating at back neck and back head. I went to many doctors, but they say it's Anxiety and stress. I took anxiety tablets nexito and anxit 0.25 but symptoms are not subsiding. Please please help.