43 days since lmp. progesterone level is 53.8nmol/l. is this level ok?

Yes: If early pregnancy is established, the corpus luteum (the functional part of the ovary in pregnancy after ovulation) produces higher levels of progesterone. In general, level of Progesterone higher than 25 indicate that corpus luteum function is adequate. Progesterone from the corpus luteum is required to maintain pregnancy until 12-13 weeks when the placenta takes over.