So confused

Got 4 BFPs on the 27th of November.

According to my period, I should have been about 6 or 7 weeks.

Went to the er for abdominal pain this weekend and they said gestational measured at 5 weeks on ultrasound (I should have been 8 weeks at that point)

They drew blood and my hcg was at 4800.

Went in 2 days later for repeat bloodwork, my hcg was 6900. So increasing but not doubling. I figured it was going to be a miscarriage. Then one day later I had more labs done and my hcg more than doubled in one day.

Has anyone experienced this before? Is this pregnancy viable? Ugh. I’m so confused. I don’t even know how I would be 5 weeks pregnant....