46 yrs. starting having period every 2 weeks off and on for last year. doc did pap smear, thyroid chk & ultrasound. all normal. am i in pre-menopause?

Yes, very likely: Women start getting into Menopause between 45-50 years of age. Due to diminishing estrogen s(female hormones) the periods become irregular and may have decreased or even increase in blood flow. So I would not worry. But let your gynecologist guide you as she may recommend an endometrial biopsy or D&C to make sure that your uterus lining is healthy and free of cancer.