Hi Donna,  I realise you know your own body better than anyone and probably could make a good guess as to what meds you require but I also don’t think you should have that responsibility as you need professional help and advice at this time!  Everyone’s pregnancy is different, so it is almost impossible for you to make judgements as to whether your symptoms are due to the  cortef dose or are just due to the pregnancy itself.   Advice varies from doctor to doctor but in general (in the UK anyway) both glucocortidoid and mineralocorticoid doses do not need increasing until the third trimester (as long as the mother continues to feel well). 

As for lowering the dose, I really do not feel that was sensible at this time and think you are right to question this.  You deserve good care, as does your baby, so if you can’t find a more experienced doctor, make sure your current one is aware of your symptoms and concerns and insist he monitors you properly to ensure your pregnancy progresses normally and you keep well.  Make a nuisance of yourself, if need be!  Take care and good luck!