HCG and progesterone levels.. 5-6 weeks Micronized pills

Was wondering if anyone could help me out with this.. did my first HCG test on Dec 2nd and those came back at 592. Second round of HCG and progesterone levels on Dec 8th came back at 5264 and 12.7, nurse said I'm around 5-6 weeks pregnant and everything with my HCG levels look good, however they don't like how low my progesterone levels are so they put me on Micronized 100mg 2x/day. Does this medication work good? Should I be worried about anything? My OB has me scheduled for an ultrasound tomorrow also which freaks me out even more. Any encouraging words will be greatly appreciated!