What counts as a period?

So I'm taking Progesterone and I have to do a Day 3 of period ultrasound. So if heavy spotting (enough for a pad or menstrual cup, not enough for a tampon) counts, then tomorrow is day 3.  But if only real periods count, then I have a few days still. 
​And on a side note, did anyone with Progesterone start their period before the 10 pill days were over?  

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