I, too, was told by my Dr. that thye first day of full flow is CD1.
Four days of spotting sounds like breakthrough bleeding. This happened to me this summer - the first time in my life - my ultrasounds in May showed a functional cyst and I didn't ovulate. My hormones were out of whack for almost 2 months.
I would suggest contacting your Dr. to see what is going on. It's easy to determine through ultrasound and bloodwork. Good luck:)
I was told that cd1 was full flow and not spotting. I'm not sure about when you spot for 4 days. I would call your RE and ask that question.