What Is The Right Dosage Of Propranolol For Fluctuating Heart Rate?

I ve taken propranolol HCL ER 120 mg for about seven years... I just had a baby and my resting heart rate has dropped from the 80s and 90s to the 50s and 60s ....my doctor reduced my medication to 8 i ve been on the reduced dose of 80 mg for about a week now my doctor says I can either stop the medication or take it every other day- is this safe? my heart rate is still in the 50s/60s and I feel cold and tired.