thank you for your query.
The medications you are taking are appropriate, however I hope there was some past or present high risk factor in the pregnancy
as you are being high doses of B HCG
to support the pregnancy.
The anechoic area you mention could be a corpus luteal cyst
which is common in pregnancy.
Other ovarian cysts also are likely, and for that I need further details of the ultrasound
Most ovarian cysts, particularly corpus luteal cysts , are likely to regress as the pregnancy advances, however if it does not, there are chances of torsion ( twisting ), infection etc.
Please get back with detailed information for further consultation.