Will Metformin 500 Help Avoid Miscarriage?

Hi, I am a PCOS case since more than 10 yrs but conceived with one month of starting Metformin this time. Already a mother of 1 child (6 yrs) and it was a regular pregnancy and normal delivery but 18 days in advance of EDD. My doc advised to continue Metformin 500 SR till delivery and also susten 200 till atleast 24 weeks... Need views .. after I m taking this medicines I feel very weak. sugar diary maintained for 7 days shows fasting (below 85 ) and PP (below 100 mostly) very well in control . Gynaec says I m giving Metformin to avoid Miscarriage. . Pls suggest whether I really need these 2 medicines.. I m also on thyrox 100 mg (before preg dose 88mg).. thyroid since 10 yrs as well.