Is there any reason that I should be braycardic 8 weeks post partum cardio myopathy and thyroid already ruled out, resting hr irregular and in 40-50

Depends. depends on whether you are on meds which could slow your heart- but in general, if you have dizziness or short of breath or if is your heart rate is irregular- you should follow up with your doctor.
Low Hr. Low heart rate in otherwise healthy young women is not a cause for concern unless there are other symptoms like dizziness fainting or weakness.