Hi Victoria, welcome to the site!
I am a student midwife so have some knowledge, but there are also some qualified midwifes on here with far greater knowledge and experince than I!
Firstly I am sorry to hear that your baby daughter was stillborn, that must have been a very difficult experince and it is only natural that it will impact upon your worries and concerns for this pregnancy.
Did you have GD last time? You don't say you did, so I assume not, huge apologies if I have misunderstood. Metformin, whilst is not a new drug in treating diabetes has only just started being used in pregnancy. Women on metformin with pre-existing diabetes were taken off oral anti-diabetics and put on insulin during pregnancy as its safety as unknown. I actually know very little about the use of metformin in diabetes and have yet to care for a woman on this regime. I have only read a little around it, but from what I have read, it looks like the outcomes are really good and possibly even better than treatment with insulin as far as outcomes for the baby. The other importnant thing is that you still maintain a good diet and avoid high sugar content foods.
The GD if controlled should not make your baby sick. If sugar levels are elevated then this can cause extra growth and can cause problems after delivery as the baby will be producing extra insulin to cope with the elevated levels, which it doesn't need once born, so can 'hypo', but your baby will be monitored in hospital. Good control should prevent this, plus early feeding.
Finally, as much as you can, try and enjoy this pregnancy too. Your diabetes and your baby are being monitored, if you are unsure of anything, make sure you ask for things to be explained, again and again if thats what it takes to reassure you. If you come away from an appointment unsure, take a notebook with you and write down everything or any questions and you can speak to your midwife and get her to explain them to you.
Wishing you all the best for the remainder of this pregnancy
Nemo. x
Have you been able to speak your team regarding your concerns?