Hormones are weird. In my last pregnancy my progesterone was also lower (7), and my thyroid went wacky during pregnancy so I was on meds for it. This pregnancy my thyroid is totally normal (I didn't get my progesterone checked so I don't know if it's higher). I also had very low, slow rising HCG with my last and this time it's very high. No idea why!
From my experience though, a new pregnancy can be like hitting the reset button. All 3 of my pregnancies have been different!