I haven't dealt with fibroids myself, but honestly the side effects you're describing sound pretty tough to manage on top of pregnancy nausea already. Since your doctor isn't open to adjusting the dose and you're struggling, it might be worth going back to them with a detailed log of how the symptoms are affecting you day-to-day so they can see the full picture and reconsider if there are other options that could work better for you. The thing is, Utrogestan is prescribed for a reason in your case, but if the trade-off is making your pregnancy miserable and they haven't explained why lower doses won't work for your specific situation, that's worth pushing back on gently with your PD or OB.
CH Ng