Hello and thank you for using HCM.I carefully read your question and I understand your concern. You should not worry about. I will try to explain you something and give you my opinion. You should know that normal heart rate ranges between 50-100 beat for minute.When it exceed 100 beat for minute in normal sinus rhythm we talk about sinus tachycardia. During tachycardia you might experience palpitation, flattering sensation, anxiety, difficulties in breathing deeply. There are different causes of sinus tachycardia from simple emotional stress, coffee or energy drink consumption, patologyes like anemia, hyperthyroidism, electrolyte imbalances or cardiac anomaly,active infections ect. Previous breastfeeding has not to do whith this symptoms. If I was your treating doctor I will recommend some examination like a cardiac echo ,a full blood analyze, your thyroid hormones and a holter rhythm monitoring to evaluate your mean frequencyes and to exclude any arythmia. After all this we can better judge how to deal and if it is necesary to treat medicaly. Hope I was helpfull. Best regards, Dr.Ervina