If you are suffering from hypothyroidism
then the medicine required is levo thyroxine
Since you are not being treated for hypothyroidism,you are gaining weight and also not getting pregnant.
PREGNAVIT tab is just a combination of FOLIC acid
and VIT D and it is not going to help in your hypothyroidism.However there is no need to stop this medicine.You must change your doctor and take proper medicines for hypothyroidism.