Worried?

Ultrasound went great today (8w2d). The Little Nugget is looking more and more like a baby and less like, well... a nugget. Heart was beating away (Dr. Cold still wouldn't give me a beats per minute amount) and things measured right on track. Dr. Cold seemed optimistic and told me to it was time to start thinking about my OB and making an appointment. All very exciting news. 


Then I got a call from them a couple hours ago indicating my progesterone levels (tested today) had dropped quite a bit. I have been on 1cc nightly (PIO) from the beginning and in recent weeks my progesterone levels had been increasing on their own! I was under the incorrect assumption that maybe the baby had actually begun producing it already (which I heard today doesn't happen till 10 weeks). My weekly progesterone levels have been 26, 27, 30, 37 and today... 26. They like to see the number over 20 so it is still in range. But why did it drop so much? Is this my indicator I might miscarry? I know progesterone levels can drop as a precursor. Dr. Cold instructed us to increase our nightly dosage from 1cc to 1.5cc. This has me worried. He stated he wasn't concerned about the drop in levels, but then instructs us to raise our dosage? 


Why are these numbers fluctuating? I am not jumping off the cliff just yet... but worried. Why must we be so fearful during these exciting times?